Qualitative modelling for the development of a sustainable management strategy for the Peruvian scallop Argopecten purpuratus (Lamarck 1819)

• 1. This study is the first attempt using Levins's Theory (loop analysis) in order to develop a sustainable management for the scallop, Argopecten purpuratus, fishery in Peru during El Niño‐Southern Oscillation events (ENSO) and upwelling conditions. Based on this theoretical framework, it was possible to estimate the local stability for each of these model systems and to follow the qualitative changes of the variables in response to external factors.
• 2. Based on our results, we suggest the following management policies to be implemented: (1) during ENSO events the size at the first capture of the scallops should be >70 mm and (2) the increase in the number of fishermen during ENSO events must be prevented. Both measures increase the sustainability of fishery under ENSO and upwelling conditions. The ecological models predict that during ENSO and upwelling events, any management strategy to increase the recruitment of the scallop would not have a positive impact on the adult stock.
• 3. Finally, we suggest that more efforts must be focused on the development of extended eco‐social models, which incorporate further social and economic variables, increasing realism of the abstractions for this fishery activity.

Copyright © 2002 John Wiley & Sons, Ltd.     

Trophic mass balanced models and dynamic simulations of benthic communities from La Rinconada Marine Reserve off northern Chile: network properties and multispecies harvest scenario assessments

• 1. Mass balanced trophic models and dynamic simulations of two benthic ecological systems from La Rinconada Marine Reserve (Antofagasta Bay, SE Pacific) were constructed.
• 2. The scallop Argopecten purpuratus is the most important benthic resource in La Rinconada Marine Reserve, followed by the carnivorous snail Thais chocolata, and the filter‐feeder bivalves Tagelus dombeii and Transennella pannosa.
• 3. Information on biomass, P/B ratios, catches, food spectrum, consumption, and dynamics of commercial and non‐commercial species was obtained and examined using Ecopath with an Ecosim software package.
• 4. The bivalves A. purpuratus and T. dombeii represented the most abundant compartments in the studied subsystems. Of the carnivores, the snail T. chocolata was dominant, followed by the crabs Cancer spp. and the functional group of large epifauna.
• 5. The two subsystems presented similar values of system throughput. The mean trophic level of their fisheries also reached similar magnitudes (2.0), showing that the harvests in each system concentrated on secondary producers. Likewise, both subsystems presented similar A/C ratios (29.9 and 30.3), suggesting that they were immature.
• 6. The results obtained using mixed trophic impact (MTI) and Ecosim (increasing the fishing mortality F_i by four times) showed that only four species propagated the highest direct and indirect effects. Coincidentally, these species are the most economically important and the changes produced by the scallop A. purpuratus are noteworthy.
• 7. With regard to the system recovery time (SRT) estimates, only three species or functional groups presented the highest magnitudes, from highest to lowest: the sea star Luidia magallanica, the scallop A. purpuratus, and the crabs Cancer spp.
• 8. The topological keystone indexes of Jordán and Libralato had divergent results. According to Jordán's index, the keystone species were L. magallanica, Cancer spp., and detritus; whereas Libralato's index showed phytoplankton to be the keystone species.
• 9. Based on the results obtained, it is concluded that trophic mass balanced models and simulated management scenarios have considerable value for planning interventions and manipulations or for planning more sustainable management strategies in La Rinconada Marine Reserve. Copyright © 2009 John Wiley & Sons, Ltd.

     

Human impacts on the endangered fan mussel,Pinna nobilis

1. Pinna nobilis is a sensitive and vulnerable species and is hence considered a good indicator of anthropogenic pressures on marine ecosystems.
2. This study provides novel data on the density and distribution of endangered P. nobilis on the Turkish coasts. Threats to the status of P. nobilis, including by‐catch and illegal collection, were assessed, as was the general awareness of people about the endangered status of fan mussels.
3. The data sources consisted of direct observations from diving surveys and the local ecological knowledge (LEK) of fishers and scuba‐divers.
4. Results demonstrated that the density of P. nobilis significantly changed with environmental parameters, such as depth, and among different sampling areas. The number of damaged individuals was lowest in the areas that were distant from human influences such as ports and tourist beaches. The density estimations of P. nobilis across a wide geographic area around the Turkish coasts revealed that the density of fan mussels was highest around western coasts in comparison with southern coasts.
5. Fishers and divers indicated that the population of this species has decreased during the last decade. The main causes of this decline were suggested to be the impacts of fishing gear, poaching, pollution, and boat anchoring. The highest volume of by‐catch was estimated to be taken by trawls. In general, the knowledge and local awareness of the conservation importance and status of fan mussels was poor.
6. The study has identified those areas where fan mussels occur at a high density, and hence may indicate areas for possible conservation protection status. Second, areas exposed to the illegal harvesting of fan mussels were highlighted. Societal concern would benefit from educational activities to raise awareness of the ecological importance and conservation needs for fan mussels in Turkey.

     

Status of the hammerhead shark (Carcharhiniformes: Sphyrnidae) fishery in Indian waters with observations on the biology of scalloped hammerhead Sphyrna lewini (Griffith & Smith, 1834)

1. Hammerhead sharks are represented by four species in India's marine fishery – Sphyrna lewini, Sphyrna mokarran, Sphyrna zygaena and Eusphyra blochii. This paper describes the hammerhead shark fishery in India during 2007–2018 and summarizes observations on the biology of S. lewini exploited along the Indian coast.
2. Hammerhead sharks are caught by trawl nets, gillnets, seines and line gear, mostly as bycatch. Annual average landing of hammerhead sharks during 2007–18 was 639 t, with a low of 290 t in 2018, of which S, lewini was the dominant species, comprising 95% of landings. Hammerhead sharks formed nearly 1.31% of the total elasmobranch landings. About 54% of hammerhead sharks were landed by trawlers.
3. Length range of S. lewini in regular landings was 36–300 cm total length (TL). The dominant size class was 30–100 cm TL; 79.5% of males and 83.2% of females measured between 40 and 100 cm TL. Length–weight relationship was derived as W = 0.0218*(L)^2.634 and W = 0.0131*(L)^2.769 for males and females, respectively.
4. Overall sex ratio (F: M) was 1.3:1; below 100 cm TL, the sex ratio was skewed in favour of females. The length at first maturity of males was estimated as 168 cm. The length at first maturity of females was estimated at 239.6 cm. Fecundity ranged from 12–40, size at birth was 36–45 cm TL. Bony fishes were the preferred prey, followed by cephalopods.
5. The S. lewini landings in India are dominated by juveniles and threatens sustainability of the stock. Capture of juvenile sharks can be excluded to a considerable extent through strict implementation of minimum legal size of capture, and a conservative minimum legal size of 220 cm is suggested for this species in Indian waters. Identification of recurring juvenile aggregation grounds, their spatio-temporal closures, gear restrictions and greater stakeholder awareness could lead to conservation of the resource and a sustainable fishery.

     

Differential response to disturbance factors for the population of sympatric crocodilians (Gavialis gangeticus and Crocodylus palustris) in Katarniaghat Wildlife Sanctuary,India

1. Katarniaghat Wildlife Sanctuary along the Indo‐Nepal border in India harbours a well‐known breeding gharial (Gavialis gangeticus) population in its global distribution range together with a substantial population of breeding muggers (Crocodylus palustris). However, no systematic information on size and structure is available for either of the species' populations in the protected area.
2. This study was undertaken in winter and the ensuing summer of 2010–2011 to estimate the relative population density and structure of the two crocodilian species and to examine the effect of various disturbance factors, with the main focus on the effects of tourism and illegal fishing on the behavioural attributes of the two species.
3. Five daytime surveys were conducted from December 2010 to April 2011. Relative density based on encounter rate (number per 20 km) was highest for gharial juveniles followed by gharial adults and gharial sub‐adults in all the five surveys. Muggers, on the other hand, showed the opposite trend, with the lowest encounter rate being for juveniles, followed by sub‐adults and adults. The encounter rate of both species declined with increase in the mean ambient temperature from December to April.
4. The river habitat was divided into 2 km segments and disturbance factors were recorded at intervals of 100 m on both river banks. Wariness was taken as an indicator of response to disturbance caused by human beings and was measured from mechanized boats used for tourism and non‐mechanized boats used for illegal fishing.
5. Segments with sandbars, in spite of moderate to high disturbance rate, were preferred for basking by both species. In conclusion, with suitable habitat for basking, gharials and muggers were observed to tolerate moderate levels of disturbance. Wariness resulting from disturbances from the non‐mechanized boats was higher than that from the mechanized boats. Gharials tend to avoid humans, possibly with age/size acquired experience and knowledge, whereas muggers become more tolerant to human presence with increased age/size.
6. Despite many disturbance factors, the crocodilian population in Katarniaghat Wildlife Sanctuary is doing relatively well compared with populations in other habitats in India. With the involvement of local stakeholders and strict implementation of forest laws, the habitat can be further improved and a healthy gharial population can be ensured.

     

Can patch size and patch distance improve the recolonization of mussel‐seed beds exploited for aquaculture?

1. Industrial‐scale exploitation of mussel seed from the rocky intertidal of north‐western Iberia is known to be detrimental for many organisms that live on or among the competitively dominant Mediterranean mussel (Mytilus galloprovincialis).
2. Searching for practices that may ameliorate the damage caused by mussel‐seed harvesting, the influence of two properties of the exploitation (patch size and patch distance) on the recolonization of the intertidal assemblage was assessed using a split‐plot design, replicating the techniques used by professional collectors. Patch recolonization was monitored by monthly records of the cover of sessile and sedentary organisms within and outside clearings throughout the official closed season (7 months).
3. Patch distance and patch size had a moderate influence on recolonization. Regardless of size and/or distance, richness and diversity stayed below control values until the end of the study, whereas total coverage was significantly smaller in the smallest patches than in control plots, but it recovered to control values in medium and large ones. Patch separation had a mostly non‐significant effect on assemblage attributes, except for a slightly greater richness and diversity in patches cleared close together than when they were apart.
4. Larger, close patches were more readily recolonized than smaller, isolated ones, possibly because the neighbouring herbivores had a negative impact during the early recolonization of the open space during the season when the shore is closed to commercial seed mussel harvesting. Nonetheless, the recolonizing assemblage consistently displayed a distinctive species composition until the end of the study, in part because clearings favoured the arrival of early colonizers, such as Ulva spp., Chthamalus sp., or Porphyra umbilicalis.
5. The consistently distinctive species composition of the recolonizing assemblage suggests that time—a too short closed season—rather than patch size and/or distance is the major obstacle to a more complete recovery of mussel‐seed exploited beds.

     

Strategies for enhancement of natural bay scallop, Argopecten irradians irradians, populations; A case study in the Niantic River estuary, Connecticut, USA

We investigated strategies to enhance populations of bay scallops,Argopecten irradians irradians (Lamarck, 1819), in a presumablyrecruitment-limited natural habitat. At present, the Niantic Riverestuary supports only a minor bay scallop population that is harvestedrecreationally. Three enhancement strategies were evaluated; (1)collection and redistribution of natural spatfall, (2) introduction andover-wintering of hatchery-reared stock into natural habitat to providenew spawning stock, and (3) over-wintering of hatchery-reared stock insuspension culture for creation of mobile spawner sanctuaries. Anassessment of natural bay scallop recruitment in the Niantic Riverconducted in 1997 indicated that few spat were found, they were widelydispersed within the river, and peak spawning occurred in late July1997. Direct re-seeding was evaluated as an enhancement measure byplanting hatchery-reared scallops ( 38 mm shell height) insmall-scale, 100-m² plots at different times and densities.Time of planting and the inferred predation intensity were major factorsaffecting survival; whereas, planting density had no significant effect.Approximately 9,000 scallops (35–45 mm shell height), broadcastwithin an eelgrass bed in November 1997, had high over-winter survivaland underwent gametogenesis and spawning during 1998. Of 26,000 bayscallops ( 45 mm shell height) over-wintered in suspensionculture from 1998–1999, approximately 60–80%survived, and these scallops spawned in mobile sanctuaries, during thesummer of 1999. There is good potential for using aquacultural methodsfor enhancement of bay scallop populations when natural recruitment ispoor and habitat and environmental conditions are not limiting.     

Declining size of adults and juvenile harvest threatens sustainability of a tropical gastropod,Lobatus gigas,fishery

1. Queen conch (Lobatus gigas) is a large herbivorous gastropod, found across the Caribbean, which forms the basis of important dive fisheries. Conch have a two‐phase shell growth pattern, first in shell length (SL), which ceases well before maturity, followed by growth in shell lip thickness (LT) into maturity. This growth pattern must be considered in determining the ideal size and associated maturity for sustainable harvest.
2. Shell morphology, sex organ development and soft tissue masses indicated that mature adult conchs at Glover's Atoll, Belize, were those with thick shell lips (≥10 mm), eroded shells and heavier soft tissue masses. Therefore, SL‐based regulations cannot serve as a proxy for maturity and harvest. The use of inappropriate minimum size limits (SL = 178 mm, 85 g market clean meat mass) has allowed significant juvenile harvest and the fishery appears to have truncated the SL size distribution of conchs with a flared shell lip (i.e. adults) over the last 15 years.
3. The reduced SL observed in lipped conchs may lead to a significant impact on the reproductive success of the population as well as diminished economic yield from the fishery, as smaller adult conchs of the same age have lower gonad and meat weight. We believe this to be the first documentation of a decline in the SL of adult queen conchs, and that the SL‐based size limits have contributed to this decline.
4. Refinement of the individual size‐based regulations for conch in Belize to LT will probably facilitate local recovery as well as regional harmonization of regulations. Future research in Belize should include movement dynamics of conch in relation to replenishment zone size and spillover as well as the importance of deep‐water conch to shallow‐water recruitment, which is thought to be limited.

     

Gene pool and connectivity patterns of Pinna nobilis in the Balearic Islands (Spain,Western Mediterranean Sea): Implications for its conservation through restocking

1. Pinna nobilis is an endemic bivalve of the Mediterranean Sea, and a vulnerable species registered as endangered and protected under the European Council Directive 92/43/EEC and Barcelona Convention.
2. In early autumn 2016, a mass mortality event impacted P. nobilis populations in the south‐western Mediterranean Sea, including the Balearic Islands. At the time of this study, P. nobilis still maintained high population densities along the Balearic coasts (Western Mediterranean).
3. This study evaluated the connectivity of P. nobilis post‐larvae and adults in seagrass habitats around the Balearic Islands and identified its source and sink populations. These objectives were reached through a multidisciplinary approach including population genetics (10 microsatellites) and hydrodynamic modelling.
4. High genetic diversity was found and significant genetic differentiation (inferred by fixation index F_ST) was detected between post‐larvae samples, but not between adult populations. Significant genic and genotypic differentiation was recorded for adults and post‐larvae.
5. This pattern was confirmed by correspondence analysis using allele frequencies. The genetic connectivity pattern was consistent with marine currents and dispersal models.
6. This work not only improves knowledge of the P. nobilis gene pool in south‐west Mediterranean populations and their connectivity patterns, but is also crucial to help evaluate the possibility of recovery from source populations and the possibility of restocking programmes, as well as provide a solid base to establish effective marine reserve networks.

     

The survival of hatchery‐origin pinto abalone Haliotis kamtschatkana released into Washington waters

1. Wild populations of pinto abalone (Haliotis kamtschatkana) in Washington State have declined by 97% since 1992, despite a fishery closure since 1994. No recruitment has been detected recently, indicating probable reproductive failure due to low densities. A pilot programme placed a total of over 11,000 hatchery‐origin juveniles, age 18–22 months, at 10 sites in the San Juan Islands.
2. Observed (naive) year 1 survival averaged 10.2% (0–23% range) and was most influenced by site compared with lineage or size‐at‐outplant. Families survived in the approximate proportions that they were outplanted, and there was little support for an effect of size‐at‐outplant on survival.
3. Detection was low due to the small chance of sighting individuals on complex substrate. When derived from repeated sampling, an upper bound on naive detection rate averaged 0.38 and increased with size. When derived from a closed capture–recapture model, average detection was estimated at 0.19.
4. Growth was highly variable and confounded with detection, but an average 3.4% of detected outplants across all sites (0–7.5% range) had reached reproductive size in 2017.
5. A state‐space model of exponential population growth was modified to account for imperfect detection and yielded an estimated density of abalone for each survey. Seven out of eight sites included in the model remained above a target abalone density of 0.3 m^?2 throughout the project.
6. The majority of tagged abalone made little net movement over weekly and annual timescales, although some emigration likely reduced survival estimates.
7. The restoration programme is transitioning from a pilot phase to a production phase, including optimization of hatchery and outplant processes. Existing well‐performing sites will receive additional cohorts every 4–5 years to maintain aggregation densities. New sites will replace poorly performing ones, although this is hampered by a poor understanding of the mechanisms behind site performance.

     

Maturity assignment based on histology‐validated macroscopic criteria: Tackling the stock decline of the Mediterranean swordfish (Xiphias gladius)

1. Effective stock assessment relies on the evaluation of the reproductive potential of a population, but this is often achieved using fast, inexpensive, and inaccurate macroscopic indicators of gonadal maturity. Indeed, this approach suffers from high error rates as a result of misclassification and operator errors. Although histology is considered the gold standard to assign reproductive stages, it represents a time‐consuming and expensive method. Therefore, cost‐effective approaches are currently needed to assess the species‐specific reproductive potential and define the correct size at first maturity (L₅₀).
2. In the present study a histology‐calibrated method based on the gonadal index (GI) was developed to assign maturity stages to the overfished Mediterranean swordfish (Xiphias gladius), supported by histological classification of gonadal development, an estimation of L₅₀, and an analysis of the reproductive output of this species.
3. The performance of this new method had an overall agreement of 90% with histological data, and the L₅₀ calculated by the GI‐based method compared with histology analysis was not statistically different (p > 0.05). Moreover, in order to apply this method without bias, a thorough validation of the relationship between length and gonad weight was carried out and the suitability of the GI to compare individuals of different size and maturity stages was confirmed.
4. The present findings provide a comprehensive picture of the patterns characterizing Mediterranean swordfish reproduction and a promising method to assign maturity stages based on a macroscopic indicator. This method has the potential to be extensively applied during routine fish sampling activities in the field because of its simple requirements.

     

Updated abundance estimates for common bottlenose dolphins (Tursiops truncatus) inhabiting West Bay,Texas

1. West Bay is located along the south‐west portion of Galveston Bay, Texas, and has been delimited as a bay, sound, and estuary (BSE) common bottlenose dolphin (Tursiops truncatus) stock area under the Marine Mammal Protection Act of 1972. The most recent abundance estimate available for the West Bay BSE stock is from 2001 and is considered outdated for management purposes.
2. This study provides an updated abundance estimate using photo‐identification capture‐mark‐recapture (CMR) data collected from West Bay during the winter of 2014 and summer of 2015. The CMR data were analysed using both Pollock's robust design models and Poisson‐log normal mark‐resight models.
3. Differences between the model types are discussed, and the abundance estimates derived from the mark‐resight models are recommended for management use (50.63 [unconditional SE 2.23] in the winter and 44.36 [unconditional SE 1.18] in the summer).
4. Whereas the updated abundance estimates are higher than the previously reported estimates, which varied between 28 and 38, they still indicate that West Bay supports a small population of bottlenose dolphins. As a result, the West Bay BSE stock should be closely monitored for impacts, particularly those related to human caused stressors.

     

Dependence of recruitment on parent stock of the spiny lobster,Panulirus argus,in Florida

Despite management practices to achieve sustainability, commercial landings for Florida spiny lobster (Panulirus argus) have experienced a drastic decline (57%) since 2000. This is cause for concern not only for economic reasons, but for issues of sustainability. An annual index of P. argus post‐larval (puerulus) abundance, estimated with a generalized linear model with significant mean sea‐level effects, shows a 36% decrease in annual puerulus supply since 1988. In addition, local Florida spawning stock biomass estimated from an age‐structured sequential population analysis decreased 57% since 1988. Puerulus abundance follows a highly correlated (R = 0.76) trend with a 12‐month delayed spawning stock abundance, which supports the contention that the Florida spawning population is a significant contributing factor to post‐larval recruitment in Florida. Residuals about the puerulus on spawning stock abundance function follow closely an interannual North Atlantic Oscillation Index signal. This residual effect is thought of as a secondary regional population effect on Florida puerulus recruitment. The Florida spiny lobster stock is exploited with no fishing mortality controls due to the Pan Caribbean recruitment concept adopted in Florida spiny lobster management. Therefore, the potential of recruitment overfishing exists if fishing mortality controls to protect local spawning stock abundance, such as catch quotas, are not introduced.     

Air-breathing ecology of Arapaima sp.: Conservation implications for an imperilled fish

1. Arapaima (Arapaima sp.) are highly overexploited fish endemic to the Amazon basin. Because the fish are obligate air-breathers, it is possible to use surface-breathing events to count individuals visually for population censuses important for conservation, yet uncertainties remain about body size and environmental influences on air-breathing intervals, and thus count accuracy.
2. This study examined relationships between breathing intervals and environmental parameters (e.g. water temperature and transparency) and body size for radio-tagged arapaima (n = 12) in an upland river-floodplain (Lake Ayapuá, Amazonas, Brazil). Generalized additive mixed models were used to evaluate environmental, size, and behavioural correlates of breathing intervals.
3. Temperature was the most influential predictor of air-breathing intervals, followed by body size. The shortest breathing intervals were associated with consecutive ‘aggressive’ breaths while the longest breathing intervals had consecutive ‘calm’ breaths. Type of breath, size, and temperature predictors revealed that breathing intervals ranged from 4 to 46 min and were not significantly different among life stages (  = 15.9 min for sub-adults and adults (>1 m);  = 14.8 min for juveniles (<1 m)).
4. Whereas the current population census method uses fish counts in 20-min intervals, this study found that 15% of observed breaths, and two thirds of fish, took longer than 20 min to breathe. These findings were obtained in relatively cool-water environments, so it is recommended that future population census methods consider water temperature (e.g. extend intervals used for counts in cooler waters), which may improve the accuracy of census counts and thus further enhance arapaima conservation efforts.
5. This study demonstrated an effective method in which fundamental biological information is used to inform and improve population census methods for an imperilled fish in a region where traditional stock assessment is ineffective. Similar approaches for adaptive stock assessments could be applied to improve conservation of other air-breathing fishes (e.g. lungfishes) globally.

     

Delineating foraging grounds of a loggerhead turtle population through satellite tracking of juveniles

1. Tracking of juvenile sea turtles is a research priority to inform the protection of relevant habitats and ensure sustainable rates of recruitment into adult populations. Based on satellite tracking, mixed stock analysis, and mark–recapture studies, Drini Bay in the South Adriatic Sea, Central Mediterranean, has been confirmed as an important foraging site used by loggerhead turtles from all major rookeries in the Mediterranean subpopulation.
2. Three juvenile loggerhead turtles (Caretta caretta) from Drini Bay were tracked for 763, 364, and 211 days respectively. All turtles exhibited different movement patterns.
3. The two smaller turtles ranged widely beyond the bay. One of these (69.5 cm curved‐carapace length; CCL) used the coldest region of the Mediterranean during the first winter of tracking where mean weekly temperatures dipped below 12°C but moved southwards to warmer waters during the second winter. In comparison, the other (66 cm CCL) individual moved south to winter in warmer waters from the outset. Both individuals returned to Drini Bay during summer, demonstrating fidelity to the study site. The third turtle, which was larger (76 cm CCL), remained in Drini Bay for the duration of tracking. These results support the findings of other mark–recapture studies at Drini Bay, which have suggested that the foraging site is being used in a transient way by immature turtles.
4. All three turtles preferentially used the shallow waters (<30 m) in the south of Drini Bay. The study demonstrates a high degree of overlap between the habitat use of the three tracked turtles and that of adult turtles tracked from nesting sites, and although based on a small sample size, contributes to a growing knowledge base regarding the wider habitat use of the Mediterranean loggerhead population.

     

A new map of the tiger shark (Galeocerdo cuvier) genetic population structure in the western Atlantic Ocean: Hypothesis of an equatorial convergence centre

1. The tiger shark (Galeocerdo cuvier) is a common widespread coastal–pelagic shark species whose population genetic structure has only recently been the object of genetic studies.
2. In this study, the tiger's shark mitochondrial DNA control region was sequenced for a sample of 172 individuals from the western Atlantic and from Australia's east coast in the Pacific Ocean.
3. The results show a moderate variation in genetic diversity (h = 0.615 ± 0.038, π = 0.00184 ± 0.00021) with a strong population structure between Atlantic areas (Φ_ST = 0.28141, P = 0.00001).
4. The maternal lineage has high site fidelity, which paradoxically is coupled with connectivity across open ocean stretches to Fernando de Noronha Archipelago, which is identified as an important hotspot for this species. These results help with the understanding of what drives the displacement of this shark, at intra‐ and/or inter‐ocean basins levels, and can help inform the implementation of future conservation and management measures.
5. We recommend that the conservation of genetic diversity should be maintained at a global level and its maintenance should be pursued diligently in all populations of tiger shark. As the Fernando de Noronha region in the western Atlantic appears to contain the largest global genetic diversity of the species, this area should be treated as a marine reserve or ecological refuge for the tiger shark.

     

Repair scars preserve decadal‐scale patterns of predation intensity despite short‐term ecological disturbances

1. Recent ecological disturbances have dramatically altered the composition of rocky intertidal Pacific coast communities of North America, particularly top invertebrate predators. Predation is an important regulatory force on intertidal gastropod communities, and the depletion or loss of predators is therefore likely to have a considerable community‐wide short‐term impact. However, assessing the magnitude and nature of the resulting ecological changes may be problematic in the absence of data recording pre‐disturbance conditions.
2. Here, the effectiveness of traces of unsuccessful crab predation on gastropod shells at providing a long‐term, decadal record of predation intensity in Barkley Sound (Vancouver Island, British Columbia) was evaluated subsequent to multiple large‐scale ecological disturbances, including sea star wasting disease, abnormally high sea surface temperatures, and harmful algal blooms.
3. The frequency of failed crab attacks recorded by repair scars on six populations of the intertidal gastropod Tegula funebralis were surveyed to compare spatial patterns in predation intensity before and after disturbance (2013 and 2015 respectively). The repair frequency gradient observed in 2013 was also recorded by repair scars in 2015 (Spearman's ρ = 1, P = 0.002), and repair frequency was not affected by gastropod size in either 2013 (Spearman's ρ = 0.14, P = 0.80) or 2015 (Spearman's ρ = 0.66, P = 0.18).
4. These findings are consistent with the hypothesis that repair frequency provides decadal records of predation intensity and may be effective to establish persistent levels of predation intensity prior to disturbances in rocky intertidal habitats.

     

Upstream migration of the anadromous sea lamprey (Petromyzon marinus Linnaeus, 1758) in a highly impounded river: Impact of low‐head obstacles and fisheries

1. Fisheries and the presence of low‐head obstacles are considered major threats for anadromous lampreys, including the sea lamprey (Petromyzon marinus). Nonetheless, research is still needed to increase our understanding of their effect and to implement effective conservation and management measures. Petromyzon marinus receives conservation protection in Europe through the Bern Convention and the European Habitats Directive and is listed as ‘Vulnerable’ in Spain.
2. The aim of this study was to investigate the impact of low‐head obstacles and fisheries on the spawning migration of P. marinus in the highly impounded River Ulla (in north‐west Spain). Nineteen lamprey were radio‐tracked in 2012 and 2013, and historical data (2002–16) on fishing captures were analysed (n = 25 607) to provide a population‐level approach.
3. The retention of individuals by low‐head obstacles, including pesqueiras constructed for lamprey fishing, and extraction by fisheries at those structures, caused a significant reduction of migrants upstream of each impoundment (mean: 24% individuals per obstacle). A delay in migration (mean: 6.3 days per obstacle) seems to be an important limiting factor for lamprey conservation in this river. Thus, based on the recorded delay, lamprey would need c. 5 months to pass the 23 obstacles present before reaching the first spawning areas and 9.5 months to cover the accessible river section (45 obstacles), which is far longer than the 3–5 months of spawning migration of P. marinus in this river.
4. Consequently, obstacle removal or permeabilization should be prioritized for lamprey conservation in this river. This would reduce migration delay, the retention of individuals, and the catchability of lamprey at pesqueiras (with alternative routes to avoid traps). Basic information on fisheries management is still lacking, especially on stock exploitation rates and on lamprey population status and dynamics. Future studies should also investigate the role of lamprey exchange between basins (a lack of homing) in the resilience of lamprey populations.

     

Status of giant clam resources around Okinawa‐jima Island,Ryukyu Archipelago,Japan

1. Giant clams provide and support valuable functions to coral reefs, as well as represent a sustainable resource for traditional fisheries throughout the Indo‐Pacific region. The Ryukyu Archipelago (southern Japan) is known to be the northern latitudinal limits of giant clam distribution, but there is only limited information in the literature regarding species diversity, status, and distribution in this region.
2. In this study, we report findings from a rapid survey in 2016, the first of its kind for the Ryukyu Islands, to determine species distribution and abundance of giant clams (tridacnines) around Okinawa‐jima Island.
3. Results indicate the presence of four species with an overall density of 5.03 per 100 m², from most to least abundant: Tridacna crocea, Tridacna maxima, Tridacna squamosa, and Tridacna noae. The previously reported species Tridacna gigas and Hippopus hippopus were both absent from the surveys. The densities and distributions of tridacnines varied among species and sites, which are likely attributable to efforts in replenishing and protecting stocks of selected species.
4. The most abundant species, T. crocea, is an important fishery species in Okinawa, and has been widely cultured and restocked to augment depleted populations. In comparison, restocking efforts for less popular species, such as T. squamosa, have been limited, and their current sizes and numbers suggest recruitment constraints.
5. Given the importance of the giant clam fishery in this region and the current declines of various species (except T. crocea), further regulations should focus on the protection of larger and mature clams that function as broodstock necessary to maintain spawning and natural recruitment.

     

Distribution and habitat characteristics of three sympatric cetacean species in the coastal waters of Matang,Perak, Peninsular Malaysia

1. Coastal cetaceans in Southeast Asia are poorly studied and are particularly vulnerable to anthropogenic threats, especially in intensive fishing grounds.
2. To investigate the distribution and habitat characteristics of cetaceans in the productive coastal waters of Matang, Perak, Malaysia, boat‐based line transect surveys were conducted between 2013 and 2016.
3. The Irrawaddy dolphin (Orcaella brevirostris) was most frequently encountered at 3.87 sightings per 100 km, followed by the Indo‐Pacific finless porpoise (Neophocaena phocaenoides) at 1.72 sightings per 100 km, and the Indo‐Pacific humpback dolphin (Sousa chinensis) at 0.66 sightings per 100 km.
4. The mean group size was largest for humpback dolphins (8.4 individuals), followed by Irrawaddy dolphins (6.4 individuals), and finless porpoises (2.8 individuals).
5. Humpback dolphins exhibited a clustered distribution concentrated mainly in shallow estuarine waters (<10 m deep and <5 km from river mouths), whereas Irrawaddy dolphins were more widely distributed in farther coastal waters (<15 m deep and <15 km from river mouths), and finless porpoises were mostly found farthest from the shore in coastal waters (10–25 m deep and >15 km from river mouths).
6. The spatial distribution of the three cetaceans overlapped minimally, and this is likely to reflect the distribution of preferred prey resources, species interactions, and their differential responses to anthropogenic activities and species dominance.
7. The results from our study serve as baseline information for future research, conservation, and habitat management of these vulnerable and endangered coastal cetaceans. Conservation actions are recommended for the Matang area.