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.

     

Sea turtle by‐catch in the Mediterranean

Sea turtle by‐catch data in the Mediterranean were reviewed and analysed with fishing effort. The results indicate over 132 000 captures per year, with probably over 44 000 incidental deaths per year, while many others are killed intentionally. Small vessels using set net, demersal longline or pelagic longline represent most of the Mediterranean fleet and likely cause more incidental or intentional deaths than large vessels typically using bottom trawl or pelagic longline. When interactions, mortality, intentional killing, size (a proxy for reproductive value) and turtle populations are considered, results indicate that Mediterranean green (Chelonia mydas) and loggerhead turtles (Caretta caretta) are more affected (i) by fishing gears such as bottom trawlers, demersal longlines and set nets, (ii) by small‐scale fisheries, and (iii) by fishing in the eastern basin. Although small‐scale fisheries should be the priority target, available measures are easier to implement on the fewer large vessels. Moreover, these measures are few, and they are not implemented yet, while others should still be tested for the Mediterranean fisheries. Thus, measures for reducing captures or mortality through changing gear‐specific characteristics may help, but probably a more holistic conservation strategy aimed to an ecosystem‐based fishery management for a sustainable fishing would be the only solution for the long‐term survival of Mediterranean Sea turtle populations and their habitats. Small‐scale fisheries should manage marine resources, including turtles, in a responsible and sustainable way. Turtles may not only benefit from but can also help this process if their non‐consumptive value is fully recognized.     

Genetic structure of the exotic hard clam <Emphasis Type="Italic">Mercenaria mercenaria</Emphasis> in Tokyo Bay,determined using mitochondrial DNA

The hard clam Mercenaria mercenaria was unintentionally introduced into Tokyo Bay during the 1990s. We analysed 528 bp of partial mitochondrial DNA of the cytochrome c oxidase subunit 1 (COI) gene extracted from 135 specimens collected from populations at five sites in Tokyo Bay to determine the genetic structure of this species. Mercenaria mercenaria populations in Tokyo Bay were dominated by haplotype 1, as in the native area. Haplotype 3, which is absent in the populations north of Cape Hatteras (North Carolina, USA) was detected at all five sites. The haplotype diversity in Tokyo Bay was as high as that in the native area, except at two canal sites, while the nucleotide diversity was lower. Thirty-five new haplotypes were found that displayed only a few nucleotide differences. Pairwise F _ST values were not significantly different between any sites in the Tokyo Bay and the east coast of America, with values for all sites in Tokyo Bay clustering near the Florida populations. The analysis of molecular variance (AMOVA) results also support this result. This study revealed that M. mercenaria populations in Tokyo Bay have a high haplotype diversity and that populations around Florida may be the source region.     

Citizen science helps assessing spatio‐temporal distribution of sea turtles in foraging areas

1. Spatio‐temporal distribution is fundamental information for species of conservation concern, like sea turtles, that are threatened by anthropogenic activities at sea such as fishing. While coarse‐scale distribution information is available for several sea turtle populations, fine‐scale distribution informing on hot‐spot areas for spatial management is more difficult to obtain.
2. Here a citizen science approach involving tourism boats was undertaken to investigate the spatio‐temporal distribution of the loggerhead sea turtle (Caretta caretta) in the Pelagie Archipelago, located in a major foraging area for this species in the Mediterranean and where high fishing‐induced mortality occurs. The study was designed to provide data of absence and total sampling effort, commonly under‐reported in citizen science studies, allowing comparison among zones and periods. This was complemented by reports from fishing vessels.
3. Tourism boats reported 584 loggerhead turtle sightings during 1718 daily trips and fishing vessels reported 280 loggerhead turtles captured during 1040 fishing days. The results indicate a strong heterogeneous distribution in the Archipelago, with a low turtle occurrence around the main island, Lampedusa, where the highest human presence and activity occur. This may represent rare evidence of displacement behaviour of turtles that is worth further investigation. This also suggests that the current small marine protected area around Lampedusa has a low conservation impact. Zones with higher loggerhead turtle occurrence appear to be in the south and the west parts of the Archipelago, suggesting that spatial management would be possible when relatively small hot‐spots have been identified through specific surveys.
4. This study shows the potential of citizen science for providing preliminary information to guide more demanding and specific investigations. Such an approach may tremendously and rapidly improve the current knowledge on fine‐scale sea turtle distribution in regions with a great extension of coastlines and intensive tourist activities, such as the Mediterranean.

     

Long‐term residence of juvenile loggerhead turtles to foraging grounds: a potential conservation hotspot in the Mediterranean

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Sea turtles bycatch in the Adriatic Sea set net fisheries and possible hot‐spot identification

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Annual survival probabilities of juvenile loggerhead sea turtles indicate high anthropogenic impact on Mediterranean populations

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Characterizing environmental and spatial variables associated with the incidental catch of olive ridley (Lepidochelys olivacea) in the Eastern Tropical Pacific purse‐seine fishery

In the Eastern Tropical Pacific (ETP), a region of high fishing activity, olive ridley (Lepidochelis olivacea) and other sea turtles are accidentally caught in fishing nets with tuna and other animals. To date, the interaction between fishing activity, ocean conditions and sea turtle incidental catch in the ETP has been described and quantified, but the factors leading to the interaction of olive ridleys and fishing activity are not well understood. This information is essential for the development of future management strategies that avoid bycatch and incidental captures of sea turtles. We used Generalized additive models (GAM) to analyze the relationship between olive ridley incidental catch per unit effort (iCPUE) in the ETP purse‐seine fisheries and environmental conditions, geographic extent and fishing set type (associated with dolphins, floating objects or in free‐swimming tuna schools). Our results suggest that water temperature, set type and geographic location (latitude, longitude and distance to nesting beaches) are the most important predictor variables to describe the probability of a capture event, with the highest iCPUE observed in sets made over floating objects. With the environmental predictors used, sea surface temperatures (SST) of 26–30°C and chlorophyll‐a (chl‐a) concentrations <0.36 mg m^?3 were associated with the highest probability of an incidental catch. Temporally, the highest probability of an incidental catch was observed in the second half of the year (June to December). Four regions were observed as high incidental catch hotspots: North and south of the equator between 0–10°N; 0–10°S and from 120 to 140°W; and along the Colombian coast and surrounding regions.     

Incidental catch of marine turtles by Spanish bottom trawlers in the western Mediterranean

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Sea turtle strandings reveal high anthropogenic mortality in Italian waters

• 1. Spatio‐temporal distribution and anthropogenic mortality factors were investigated in loggerhead turtles (Caretta caretta) found stranded or floating in the waters around Italy. A total of 5938 records for the period 1980–2008 were analysed concerning loggerhead turtles measuring from 3.8 to 97 cm curved carapace length (mean: 48.3 cm).
• 2. Results highlighted the following conservation issues: (i) in the study area, anthropogenic mortality is higher than natural mortality; (ii) interaction with fisheries is by far the most important anthropogenic mortality factor; (iii) longlines are an important mortality factor in the southern areas; (iv) trawlers are the cause of high numbers of dead strandings in the north Adriatic; (v) entanglement in ghost‐gear or in other anthropogenic debris affects high numbers of turtles; and (vi) boat strikes are an important source of mortality in most areas but mostly in the warm seasons.
• 3. Results also indicate that: (vii) the north Adriatic is the area with the highest turtle density; and (viii) the south Adriatic and to a lesser extent the surrounding areas of the north Adriatic and the Ionian, are important developmental areas for loggerhead turtles in the first years of life.
• 4. Italy is in the centre of the Mediterranean Sea and borders major foraging areas for the loggerhead turtles in the region, and these results confirm previous concerns about the level of anthropogenic mortality in Italian waters. Copyright © 2010 John Wiley & Sons, Ltd.

     

Incidental capture and mortality of sea turtles in the industrial double‐rig‐bottom trawl fishery in south‐eastern Brazil

1. Incidental capture by fisheries is one of the principal threats to sea turtles. This study analysed spatial and temporal patterns of sea turtle bycatch, and estimated the direct initial mortality rate of these animals, in the industrial double‐rig‐bottom trawl fishery in south‐eastern Brazil. This is also the first attempt to relate bycatch/at‐sea mortality in bottom trawling to stranded turtles found along the adjacent coast.
2. The fishery was monitored from October 2015 to April 2018 through data collected voluntarily by the captains of eight industrial double‐rig trawlers. Two hundred and one sea turtles were captured during 9362 tows (43,657.52 trawling hours), resulting in a catch per unit effort (CPUE) of 0.0025 ± 0.0032 turtles h^?1 with a standard net of 30.5 m headrope, with no significant difference between the estimated CPUEs for licensed shrimp and demersal fish trawlers.
3. Caretta caretta (52.24%) and Lepidochelys olivacea (38.81%) were the most frequently captured species. According to Generalized Linear Models, C. caretta bycatch was significantly higher during winter, at lower latitudes (?24° to ?23°) and higher longitudes (?42° to ?40°), while the L. olivacea bycatch was significantly higher at higher latitudes (?23° to ?21°). The direct initial mortality rate of sea turtles in the shrimp trawlers was 7.65 ± 3.85%. However, none of the dead individuals subsequently released with plastic tags (n = 10) were found stranded on the coast. Mortality was not significantly related to the depth or duration of the trawling.
4. The results of this study suggest the need for improvements to the current management of the bottom trawl fishery in Brazil, moving from a species‐based to a spatial and seasonal‐based approach. There is also a need to develop turtle excluder devices adapted to local fishing conditions.

     

Forage and migration habitat of loggerhead (Caretta caretta) and olive ridley (Lepidochelys olivacea) sea turtles in the central North Pacific Ocean

Satellite telemetry from 26 loggerhead (Caretta caretta) and 10 olive ridley (Lepidochelys olivacea) sea turtles captured and released from pelagic longline fishing gear provided information on the turtles’ position and movement in the central North Pacific. These data together with environmental data from satellite remote sensing are used to describe the oceanic habitat used by these turtles. The results indicate that loggerheads travel westward, move seasonally north and south primarily through the region 28–40°N, and occupy sea surface temperatures (SST) of 15–25°C. Their dive depth distribution indicated that they spend 40% of their time at the surface and 90% of their time at depths <40 m. Loggerheads are found in association with fronts, eddies, and geostrophic currents. Specifically, the Transition Zone Chlorophyll Front (TZCF) and the southern edge of the Kuroshio Extension Current (KEC) appear to be important forage and migration habitats for loggerheads. In contrast, olive ridleys were found primarily south of loggerhead habitat in the region 8–31°N latitude, occupying warmer water with SSTs of 23–28°C. They have a deeper dive pattern than loggerheads, spending only 20% of their time at the surface and 60% shallower than 40 m. However, the three olive ridleys identified from genetics to be of western Pacific origin spent some time associated with major ocean currents, specifically the southern edge of the KEC, the North Equatorial Current (NEC), and the Equatorial Counter Current (ECC). These habitats were not used by any olive ridleys of eastern Pacific origin suggesting that olive ridleys from different populations may occupy different oceanic habitats.     

Mitochondrial DNA short tandem repeats unveil hidden population structuring and migration routes of an endangered marine turtle

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Reconstructing 290 years of a data‐poor fishery through ethnographic and archival research: The East Pacific green turtle (Chelonia mydas) in Baja California,Mexico

Evaluating historical changes in the exploitation of marine organisms is a key challenge in fisheries ecology and marine conservation. In the Eastern Pacific, marine turtles were exploited for millennia before systematic monitoring began <50 years ago. Using ethnographic and historical data, we generated a detailed reconstruction of the East Pacific green sea turtle (Chelonia mydas) fishery in Mexico's Baja California peninsula from 1700 to 1990. Sea turtles from the region's important feeding areas were a staple food source from the earliest phases of human occupation, dating back at least 12,000 years. In contrast with regions such as the Caribbean, small human populations and limited market access resulted in apparently sustainable turtle harvests until the second half of the 20th century. We found that the estimated annual catches between 1960 and 1980 exceeded the estimated annual catches of the previous 250 years by an order of magnitude, leading to the collapse of the fishery and the depletion of the green turtle population. A total ban on sea turtle captures in 1990, comprehensive nesting beach protection, and significant conservation efforts resulted in increases in breeding females on nesting beaches and catch rates in scientific monitoring on main feeding grounds since the early 2000s. This provides a positive outlook for this once‐depleted population segment. Although further research is needed to evaluate current conservation status, we have identified a date, between 1950 and 1960, which can serve as a reliable temporal reference for future evaluations of historical baseline abundance in this region.     

A fructose‐based extender protects Colossoma macropomum spermatozoa against chilling injuries

Our study assessed the efficiency of a formulated new extender in maintaining viability and morphological integrity of Colossoma macropomum spermatozoa under chilling storage. Semen was diluted in the test extender and BTS? (Beltsville Thawing Solution) and exposed to a short‐term storage at 4.6 ± 0.6°C for 96 hr. Both extenders were able to maintain 17% ± 8% motile spermatozoa by the end of experiment. Sperm dilution in test extender did not affect the morphologically normal cells (61% ± 6%) up to 48 hr of chilling, being higher than in BTS? (50% ± 6%) (p < 0.05). After 96 hr, samples kept in the test extender had 50% of normal spermatozoa, whereas those kept in BTS? presented only 38% of normal cells. Chilling storage increased the incidence of cells with strongly coiled flagella in BTS^?. Our study is the first to evaluate in detail the spermatozoa morphology as indicative of C. macropomum semen viability. The new extender was able to protect the spermatozoa against increase in coiled flagellum injuries.     

Circle hook effectiveness for the mitigation of sea turtle bycatch and capture of target species in a Brazilian pelagic longline fishery

• 1. Incidental catches by the pelagic longline fishery is a major global threat for loggerhead (Caretta caretta) and leatherback (Dermochelys coriacea) sea turtles.
• 2. The reduction of incidental capture and post‐release mortality of sea turtles in the Brazilian pelagic longline fishery, operating in the south‐western Atlantic Ocean, was investigated by comparing the performance of 18/0 circle hooks with 9/0 J‐type (control) hooks. Hook selectivity experiments were performed between 2004 and 2008, in a total of 26 trips, 229 sets and 145 828 hooks. The experimental design included alternating control and experimental hooks along sections of the mainline.
• 3. An overall decrease in capture rates for loggerhead turtles of 55% and for leatherbacks of 65% were observed when using circle hooks. In addition, deep‐hooking in loggerheads decreased significantly from 25% using J‐hooks to 5.8% with circle hooks, potentially increasing post‐release survival.
• 4. Circle hooks increased catch rates of most of the main target species, including tunas (bigeye Thunnus obesus and albacore T. alalunga), and sharks (blue Prionace glauca and requiem sharks of the genus Carcharinus), with no difference in the capture rates of yellowfin tuna (T. albacares), shortfin mako shark (Isurus oxyrinchus), hammerhead sharks (Sphyrna lewini and S. zygaena), and dolphinfish or mahi mahi (Coryphaena hippurus). On the other hand, a significant decrease in the capture rate of swordfish (Xiphias gladius) was detected when using circle hooks.
• 5. Overall, results support the effectiveness of using circle hooks for the conservation of loggerhead and leatherback sea turtles, with positive effects on capture of most target species of the south‐western Atlantic longline fishery. Copyright © 2010 John Wiley & Sons, Ltd.

     

Enhancing the TurtleWatch product for leatherback sea turtles,a dynamic habitat model for ecosystem‐based management

Fishery management measures to reduce interactions between fisheries and endangered or threatened species have typically relied on static time‐area closures. While these efforts have reduced interactions, they can be costly and inefficient for managing highly migratory species such as sea turtles. The NOAA TurtleWatch product was created in 2006 as a tool to reduce the rates of interactions of loggerhead sea turtles with shallow‐set longline gear deployed by the Hawaii‐based pelagic longline fishery targeting swordfish. TurtleWatch provides information on loggerhead habitat and can be used by managers and industry to make dynamic management decisions to potentially reduce incidentally capturing turtles during fishing operations. TurtleWatch is expanded here to include information on endangered leatherback turtles to help reduce incidental capture rates in the central North Pacific. Fishery‐dependent data were combined with fishing effort, bycatch and satellite tracking data of leatherbacks to characterize sea surface temperature (SST) relationships that identify habitat or interaction ‘hotspots’. Analysis of SST identified two zones, centered at 17.2° and 22.9°C, occupied by leatherbacks on fishing grounds of the Hawaii‐based swordfish fishery. This new information was used to expand the TurtleWatch product to provide managers and industry near real‐time habitat information for both loggerheads and leatherbacks. The updated TurtleWatch product provides a tool for dynamic management of the Hawaii‐based shallow‐set fishery to aid in the bycatch reduction of both species. Updating the management strategy to dynamically adapt to shifts in multi‐species habitat use through time is a step towards an ecosystem‐based approach to fisheries management in pelagic ecosystems.     

Incidental capture of Caretta caretta in trammel nets off the western coast of Sardinia (Italy): statistical models of capture abundance and immediate survival

• 1. Trammel nets are one important cause of sea turtle mortality resulting from incidental capture. This study presents findings over a 10‐year period during which loggerhead turtle by‐catch in trammel nets, set off the central west coast of Sardinia (Italy) in the summer months, was recorded by 17 fishing vessels.
• 2. Since the by‐catch registered represented counts of a rare event, data from the 17 vessels were used in the zero‐inflated Poisson (ZIP) model to determine the abundance of turtle by‐catch in trammel nets of the entire fleet, while a binomial generalized linear model was used to assess the probability of immediate survival for sea turtles incidentally caught in this gear.
• 3. The ZIP model quantified in about 45% the probability that 0.6 turtles have been caught by each vessel using trammel nets during summer over the 10‐year period. In addition, the model estimated a total of 916 by‐catch if the entire small‐scale fleet was to use trammel nets in the study area in the summers between 1992 and 2001, with a direct mortality rate of 69%.
• 4. The probability of immediate survival for sea turtles caught in trammel nets seems to be directly related to the size of the specimens caught; however, this relationship is plausible only when incidental capture in the net occurs shortly before gear retrieval.
• 5. The study area represents a region where the abundance of sea turtle by‐catch per vessel in trammel nets was much higher in July and August than in June and could represent a potential hot spot for the presence of juvenile loggerhead turtles, with high levels of interactions between the species and this fishing gear. Further research should better characterize the incidents of by‐catch and assess potential innovative solutions that allow small‐scale fisheries to coexist alongside sea turtles. Copyright © 2010 John Wiley & Sons, Ltd.

     

A cross‐taxa assessment of pelagic longline by‐catch mitigation measures: conflicts and mutual benefits to elasmobranchs

Elasmobranch mortality in pelagic longline fisheries poses a risk to some populations, alters the distribution of abundance between sympatric competitors, changing ecosystem structure, processes and stability. Individual and synergistic effects on elasmobranch catch and survival from pelagic longline gear factors, including methods prescribed to mitigate bycatch of other vulnerable taxa, were determined. Overall relative risk of higher circle vs. J‐shaped hook shark catch rates conditioned on potentially informative moderators, from 30 studies, was estimated using an inverse‐precision weighted mixed‐effects meta‐regression modelling approach. Sharks had a 1.20 times (95% CI: 1.03–1.39) significantly higher pooled relative risk of capture on circle hooks, with two significant moderators. The pooled relative risk estimate of ray circle hook catch from 15 studies was not significant (RR = 1.22, 95% CI: 0.89–1.66) with no significant moderators. From a literature review, wire leaders had higher shark catch and haulback mortality than monofilament. Interacting effects of hook, bait and leader affect shark catch rates: hook shape and width and bait type determine hooking position and ability to sever monofilament leaders. Circle hooks increased elasmobranch catch, but reduced haulback mortality and deep hooking relative to J‐shaped hooks of the same or narrower width. Using fish vs. squid for bait increased shark catch and deep hooking. Pelagic stingray (Pteroplatytrygon violacea) catch and mortality were lower on wider hooks. Using circle instead of J‐shaped hooks and fish instead of squid for bait, while benefitting sea turtles, odontocetes and possibly seabirds, exacerbates elasmobranch catch and injury, therefore warranting fishery‐specific assessments to determine relative risks.     

Effects of a hook ring on catch and bycatch in a Mediterranean swordfish longline fishery: small addition with potentially large consequences

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