Pelagic longline gear depth and shoaling

Temperature-depth recorders (TDRs) were attached to pelagic longline gear in the Hawaii-based commercial fishery to obtain actual fishing depths and to test the accuracy of catenary algorithms for predicting fishing depths. Swordfish gear was set shallow by typically deploying four hooks between successive floats. The observed depth of the settled deepest hook had a median value of 60 m for 333 swordfish sets. Tuna longline gear deployed more hooks between floats (mean = 26.8), and the observed median depth of the deepest hook was 248 m (n = 266 sets). Maximum gear depth was predicted from estimates of the longline sag ratio and catenary algorithms; however, depth was not predicted for all TDR-monitored sets because estimating sag ratios proved problematic. Swordfish sets had less slack in the main line and correspondingly smaller catenary angles (median = 54.2°) than tuna sets (median = 63.7°). Median values of the predicted catenary depth were 123 m for swordfish sets (n = 203) and 307 m for tuna sets (n = 198). Shallow swordfish sets reached only ∼50% of their predicted depth, while deeper tuna sets reached about 70%. These values indicated that capture depths using traditional catenary equations may be biased without the benefit of TDRs affixed to longlines. Generalized linear models (GLMs) and generalized additive models (GAMs) were developed to explain the percentage of longline shoaling as a function of predicted catenary depth and environmental effects of wind stress, surface current velocity, and current shear. The GAM explained 67.2% of the deviance in shoaling for tuna sets and 41.3% for swordfish sets. Predicted catenary depth was always the initial variable included in the stepwise process, and the inclusion of environmental information in the GAM approach explained an additional 10–17% of the deviance compared to the GLMs. The explanatory ability of the environmental data may have been limited by the scale of the observations (1° in space; weekly or monthly in time) or the geometric (transverse versus in-line) forcing between the environment and longline set. Longline gear models with environmental forcing affecting shoaling may be improved in future studies by incorporating contemporaneous environmental information, although this may restrict analyses to fine-scale experimental longlines.     

A comparison of circle hook and J hook performance in a western equatorial Atlantic Ocean pelagic longline fishery

Catch composition, catch rates, hooking location, and status at release at haulback were monitored during 81 experimental sets (launches and hauling fishing per day) in a commercial pelagic longline fishery targeting tuna in the equatorial South Atlantic Ocean. Circle hooks (size 18/0, 0° offset) and J-style hooks (size 9/0, 10° offset) with squid baits were deployed in an alternating fashion. The catch composition was not significantly different for most species between the two types of hooks, except for bigeye tuna, which showed a significantly higher proportion of catches on the circle hook (p ? 0.001) and for sailfish, pelagic stingray, and leatherback sea turtle, which had higher catch rates on the J-style hook (p = 0.018, p ? 0.001, and p = 0.044, respectively). Bigeye and yellowfin tuna showed significantly higher rates of survival at the time of gear retrieval with circle hooks, and circle hooks hooked bigeye tuna, yellowfin tuna, swordfish, and sailfish significantly more often externally than internally. Our results suggest that the use of size 18/0, 0° offset circle hooks in the equatorial pelagic longline fishery may increase the survival of bycatch species at the time of gear retrieval with minimal effects on the catches of target species.     

Mortality impact of recreational angling techniques and hook types on Trachynotus ovatus (Linnaeus, 1758) following catch-and-release

We evaluated the post-release mortality (PRM) following catch-and-release in Trachynotus ovatus, one of the main target species of north-western Mediterranean recreational fisheries. In this study, we observed the line-caught fish for 10 d in a holding tank in order to investigate the independence and impact on mortality of several explanatory variables, including fish size, surface temperature, anatomical hooking location, bleeding, hook type, and line cutting. We observed a total PRM of 24.1% and the most important mortality factor by far was the anatomical position of the hook. Anatomically deeper hooking events were highly correlated with fish size and the presence of blood during hooking injuries. The PRM obtained in this study was higher than values reported in previous studies of this species, mainly because we considered the effects of passive angling techniques. Passive angling increased the incidence of deep hooking and consequently increased mortality compared to active angling. This technique also led to an increase in deep hooking by circle hooks. Therefore, we recommend that active angling techniques be encouraged and we emphasize the need for education on the correct use of circle hooks. This study provides guidelines to managers, scientists, and anglers that will promote sustainable development of the recreational fisheries of the Mediterranean.     

Estimating post-release survival and the influential factors for recreationally caught Black bream (Acanthopagrus butcheri) in the Glenelg River, south eastern Australia

Black bream (Acanthopagrus butcheri) is the main target species amongst the estuarine recreational fisheries of Victoria, Australia. The A. butcheri fishery is managed through legal-minimum length and daily bag limits. The success of this management strategy requires that the survival rate for released fish is high. This study used the most common angling practices to estimate post-release survival and identify influential factors for undersized A. butcheri in Victoria. In total 1557 and 923 A. butcheri were caught and monitored for initial (≤1 h) and delayed (72 h) survival, respectively. Fish were caught across 3 years, with each year separated into cold and warm water periods with 8 fishing trial days in total. Only 1 of the 266 controls used to assess confinement effects died. Total survival was 95% (S.E. ± 0.8%) for shallow- and 74% (S.E. ± 3%) for deep-hooked fish and decreased as fish length increased. A post-mortem (PM) procedure was developed and showed that throat and gill injuries were the most frequent cause of deep-hooking death. It revealed that 97% of hooks left in fish remained there after 72 h and identified hooking location inaccuracies recorded at the time of capture. Total survival for deep-hooked fish was 20% higher when hooks were left in the fish. Deep-hooked fish were more likely to bleed when hooks were removed and total survival was lower for fish that bleed (58%) than fish that did not bleed (80%). Shallow-hooking rates decreased as fish length increased and were higher during warm water compared to cold water trials. The high shallow-hooking and survival rates observed suggest that A. butcheri survival in the fishery would be high, but deep-hooking has the potential to undermine the management strategy. Determining the shallow-hooking rate in the fishery would help clarify the impact of these findings at the fishery level.     

Capture time,size and hooking mortality of bottom longline-caught sharks

The primary gear type used to harvest coastal sharks in the U.S. Atlantic shark fishery is bottom longline. Recent stock assessments have found several species of coastal sharks in U.S. Atlantic Ocean waters have declined from 60% to 80% of virgin levels. To aid in stock rebuilding, alternative gear restriction measures such as reduced soak time, restrictions on the length of gear, and fishing depth restrictions have been considered but not implemented. In order to evaluate the effectiveness of some of these management measures, controlled experiments were performed using hook timers and time depth recorders, assessing the factors affecting mortality during longline capture for the four most abundant species that incurred at-vessel mortality: sandbar (Carcharhinus plumbeus), blacktip (Carcharhinus limbatus), bull (Carcharhinus leucas), and blacknose (Carcharhinus acronotus). Our results indicate that as hook time and shark size increased mortality rates for the sandbar and blacktip sharks increased. Predicted models indicated mortality rates increased steadily for the three species but appeared to increase the most after 10, 6, and 1 h on the hook for sandbar, blacktip and blacknose shark, respectively. Sandbar sharks larger than approximately 170 cm FL are more susceptible to hooking mortality. Blacknose shark mortality rates increased as hook time increased but bull shark mortality rates were not affected by any factor. The probability of a hook being bitten increased the most between 5 and 12 h after the fishing gear had been set and the mean amount of time hooks were in the water prior to being bitten was 4, 5 and 9 h for sandbar and blacknose sharks, blacktip, and bull sharks, respectively. A significant difference was found between these means for sandbar and bull sharks and between blacknose and bull sharks. Shark species were commonly caught at different temperature and depth ranges. These results could be used by fisheries management to implement restrictions of fishing depth and soak time to aid in the recovery of coastal sharks species.     

Short-term hooking mortality of three marine fish species (Sparidae) caught by recreational angling in the south Portugal

Short-term hooking mortality was evaluated for three sparid species [Diplodus vulgaris (Geoffroy Saint-Hilaire), Sparus aurata L. and Spondyliosoma cantharus (L.)] in the Algarve, south Portugal. Fishes were caught from the shore during October 2009 at a fish farm reservoir (Ria Formosa), using three different hook sizes. The relationships between hooking mortality and seven independent variables were analyzed using logistic regression models. In all, 384 fishes representing the three target species were caught during the angling sessions. The most caught species was S. cantharus (n = 181; 100% undersized), followed by S. aurata (n = 137; 89% undersized) and D. vulgaris (n = 66; 97% undersized). Mortalities ranged between 0% for D. vulgaris and 12% for S. aurata (S. cantharus, 3%). For S. aurata, anatomical hooking location was the main predictor of mortality, with 63% of the fishes that died being deeply hooked. Our results support the current mandatory practices of releasing undersized fish for the studied species, given the low post-release mortality rates observed.     

Population dynamics of Melicertus kerathurus (Decapoda: Penaeidae) in Thermaikos Gulf (N. Aegean Sea)

The east Atlantic-Mediterranean penaeid Melicertus kerathurus constitutes a valuable resource for Mediterranean fisheries. In recent years, its world production is almost totally based on the yields from Greece and Tunisia. A two-year study of prawn stock in Thermaikos Gulf (NW Aegean Sea) provided information on age, growth and mortality of the species. M. kerathurus exhibits a marked sexual growth dimorphism, with females showing an overall wider size range and greater size than males. Mean monthly size, CL_max were also in favor of females. Monthly age classes varied from one to four for females and from one to three for males, and corresponded to three generations (0⁺, 1⁺, 2⁺). New generation (0⁺) cohorts recruited into fishery in waves, from late summer to February. According to the von Bertalanffy growth curve, females grow larger than males, but there is a prominent seasonal growth oscillation in both sexes (females: CL_∞ = 62.48, K = 1.15, C = 0.87, WP = 0.16, Rn = 0.170; males: CL_∞ = 47.78, K = 1.28, C = 0.97, WP = 0.12, Rn = 0.205). Growth performance indices (φ′, φ) and longevity were in favor of females. K values for both sexes in Thermaikos Gulf are the highest reported for the species, suggesting a higher growth rate and a lower longevity. Estimated values for total, natural and fishery mortality were greater in males. In both sexes, an exploitation rate E > 0.5 was found, implying an intense fishing impact on M. kerathurus stock in Thermaikos Gulf. Intense exploitation in other parts of the Mediterranean and eastern Atlantic, along with the replacement of the species by Eritrean penaeid prawns in the eastern Mediterranean, has resulted in a severe reduction in catches, in most countries. Thus, existing stocks of M. kerathurus should be considered as potentially endangered, and species-specific initiatives towards sustainable management of this resource should be implemented.     

Insights into catch-and-release survivorship and stress-induced blood biochemistry of common thresher sharks (Alopias vulpinus) captured in the southern California recreational fishery

The common thresher shark (Alopias vulpinus) is the focus of a popular southern California recreational fishery that typically captures individuals by hooking them in the caudal fin. This technique reduces the ability for forward locomotion and the capacity for ram ventilation. This study assessed the post-capture survivorship of tail-hooked adult and sub-adult common thresher sharks using pop-up satellite archival tags (PSATs) and quantified physiological indicators of capture stress in the blood. Survival of the acute effects of capture was determined from the depth and temperature records of 10-day PSAT deployments. Survivorship estimates were based on 19 common thresher sharks [160–221 cm fork length (FL); ～67–151 kg] captured in southern California from 2007 to 2009 using recreational stand-up tackle (36 kg). Five mortalities were observed over the course of the study resulting in an overall post-release mortality estimate of 26%. All mortalities occurred in large individuals (≥180 cm FL) with fight times ≥85 min. The archived depth and temperature data from surviving sharks resembled those of previous common thresher movement studies with a diel depth distribution predominantly within the uniformed temperature surface layer. Capture induced stress parameters measured from the blood of eight additional common thresher sharks that were not tagged revealed plasma lactate and hematocrit levels that were significantly elevated with increased fight time. Similarly, all thresher sharks showed heightened heat shock protein 70 (hsp 70) values relative to those obtained from blood that was allowed to recover in vitro for 24 h. Collectively, our findings indicate that large tail-hooked common thresher sharks with prolonged fight times (≥85 min) exhibit a heightened stress response which may contribute to an increased mortality rate. These results suggest that for larger individuals the current caudal-based capture methods used in the California recreational fishery may not be suitable for an effective catch-and-release based conservation strategy.     

Interactions between sea turtles and dredge gear in the U.S. sea scallop (Placopecten magellanicus) fishery, 2001–2008

Since 2006, the National Marine Fisheries Service (NMFS) has mandated gear modifications (“chain mats”) and fishing effort reductions in the U.S. Mid-Atlantic sea scallop dredge fishery to alleviate or minimize interactions with sea turtles. Turtle interactions with gear can be defined as those that are “observable” based on standard fishery observer protocols, plus unobserved interactions, which include both quantifiable and unquantifiable interactions. Once a gear modification is in place, a turtle interaction that was once observable may become unobservable, because the gear modification successfully prevented the turtle from being captured. This paper describes turtle interactions in scallop dredge gear from 2001 to 2008, identifies gear and environmental correlates with observable interaction rates, and reports the average annual number of interactions and adult-equivalent interactions before and after chain mats were mandated in the fishery. Fisheries observer data were used to develop a Generalized Additive Model (GAM) to estimate rates of observable interactions of hard-shelled turtles. These rates were applied to commercial dredge fishing effort to estimate the total number of observable interactions, and to infer the number of unobservable, yet quantifiable interactions after chain mats were implemented. Interaction rates of hard-shelled turtles were correlated with sea surface temperature, depth, and use of a chain mat. The average number of annual observable interactions of hard-shelled turtles in the Mid-Atlantic scallop dredge fishery prior to the implementation of chain mats (1 January 2001 through 25 September 2006) was estimated to be 288 turtles (CV = 0.14, 95% CI: 209–363), which is equivalent to 49 adults. After implementation of chain mats, the average annual number of observable interactions was estimated to be 20 turtles (CV = 0.48, 95% CI: 3–42), equivalent to 4 adults. If the rate of observable interactions from dredges without chain mats had been applied to trips with chain mats, the estimated number of observable and inferred interactions of hard-shelled species after chain mats were implemented would have been 125 turtles per year (CV = 0.15, 95% CI: 88–163). Results from this analysis suggest that chain mats and fishing effort reductions contributed to the decline in estimated turtle interactions after 2006.     

Gulf menhaden (Brevoortia patronus) in the U.S. Gulf of Mexico: Fishery characteristics and biological reference points for management

Gulf menhaden, Brevoortia patronus, plays a key ecological role in the northern Gulf of Mexico and supports the second largest commercial fishery by weight in the United States. Here we describe that fishery and propose biological reference points (BRPs) for its management. The BRPs represent targets and limits of both fishing mortality rate (F) and population fecundity (Ψ), where target is defined as the management goal, and limit, a value to be avoided (F < F_Limit and Ψ > Ψ_Limit). We assess stock status relative to the BRPs by fitting a statistical catch-age model to fishery-dependent and fishery-independent data spanning 1964–2004. Results indicate that in the terminal year neither limit reference point is exceeded (F₂₀₀₄/F_Limit = 0.75 and Ψ₂₀₀₄/Ψ_Limit = 1.86). Of possible concern, however, is a recent increase in fishing mortality and decrease in population fecundity. With these trends, terminal values exceed their targets (F₂₀₀₄/F_Target = 1.16 and Ψ₂₀₀₄/Ψ_Target = 0.93), although by little relative to uncertainty in the estimates. Sensitivity analyses show these results are robust to model assumptions.     

A long-term (1667–1860) perspective on impacts of fishing and environmental variability on fisheries for herring,eel, and whitefish in the Limfjord,Denmark

This investigation reconstructs the development of major fisheries for herring, eel and whitefish in the Limfjord estuary, Denmark ca. 1667–1860, and then evaluates how their long-term dynamics have been influenced by some key fishery and environmental developments. The commercially most important fishery was for herring, Clupea harengus, which spawned in the Limfjord. This fishery underwent large changes in these centuries. High landings occurred in two periods in the early 18th and again in the early 19th centuries, when 4000–8000 metric tonnes were caught annually. In 1830, the fishery collapsed and landings were <1000 tonnes until the 1910s. Even during the 20th century using modern fishing techniques, the herring fishery never exceeded 7000 tonnes. The collapse was most likely due to unsustainable fishing practices (direct impacts on adults, juveniles, larvae and eggs). The second most important fishery of the Limfjord was the eel fishery. Eel, Anguilla anguilla, seems to have fled the fjord after a winter storm in 1825 broke the narrow Agger Tange isthmus which used to separate the Limfjord from the North Sea, and permanently increased the salinity in the western part of the Limfjord from 8 psu to 33 psu. The, so-called pulse seine fishery for eel declined rapidly following the salt water intrusion, and the population needed at least one to two generations to even partly recover. One possible technological reason for the recovery of the fishery was the 1848 invention of a new type of gear in the Limfjord which today is known as the Danish seine. However, the commercial eel fishery in Limfjord ceased by the 1980s coincident with the overall decline in European eel populations. The third fishery analyzed is the fishery for common whitefish, Coregonus lavaretus. A local population formed the basis of a substantial seasonal fishery, but the whitefish did not survive the salinity obstacle presented by the salt water intrusion in 1825. This study documents both the effects of fishing and environmental variability on collapses of different Limfjord fish species.     

Deterring coastal birds from roosting on oyster culture gear in eastern New Brunswick,Canada

An ornithological survey was conducted along the eastern coastline of New Brunswick, Canada, where oysters are cultivated in suspension using PVC bags and wire-mesh cages. Thirteen bird species and a variety of unidentified shorebirds were observed roosting on the floating oyster gear. The double-crested cormorant (Phalacrocorax auritus) was the most common species observed (47.6% of all counts), closely followed by herring gulls (Larus argentatus) and common terns (Sterna hirundo) at 18.7% and 13.0%, respectively. Birds were densely aggregated where few cages or bags had been deployed. A gear-type effect was also detected: birds were more abundant on floating cages (mean = 47.9/100 m² of exposed area, S.E. = 5.8) than on floating bags (mean = 32.8/100 m², S.E. = 1.9). The survey was followed by two experiments designed to test the effects of gear modifications on bird abundance and diversity. For bags, results indicated that shallow immersion (～6 cm below surface) and floater instability were effective deterrents to P. auritus, reducing its abundance by a 37-fold factor. For wire-mesh cages, a dented triangular structure mounted on top of floaters was a harassing physical barrier to roosting behaviour, consequently reducing bird abundances to null (or near null) values.     

Experimental harvesting of Mytilus galloprovincialis: Can an alien mussel support a small-scale fishery?

In an effort to stimulate new fisheries and address historic imbalances in access to fishing rights, there has been a recent focus on the development of small-scale fisheries in South Africa. To assess the biological viability of a fishery for the alien mussel Mytilus galloprovincialis, an experimental fishery operated by two impoverished coastal communities was initiated. Harvesting took place on a rotational basis at three sites, nested within four locations. At each of these 12 sites, 5 treatments were undertaken to span a spectrum of harvesting intensities (F = 0, 0.3, 0.6, 0.9 and a once-off total removal). A dynamic biomass-based fisheries model was developed to predict changes in exploited populations over time. Monthly maximum sustainable yield (MSY) estimates peaked at 1560 kg per 100 m of shore in March–April and September–October, but dropped by two orders of magnitude to 15 kg per 100 m of shore during the remainder of the year. The two peaks in MSY corresponded to the peak spawning periods of M. galloprovincialis along the South African west coast. Consequently, harvesting will only be viable if focused within two seasons spanning the peaks in MSY. Under these conditions, a range of harvesting intensities between F = 0.1 and 0.3 would permit long-term biological sustainability of a fishery. If implemented, this would represent the first instance of a marine invasive species being utilised to achieve socio-economic goals in South Africa.     

Population dynamics and fishery benefits of a large legal size of a pelagic sportfish,the Talang queenfish,Scomberoides commersonnianus,in northern Australia

The life history of an increasingly important pelagic commercial and sport fish, the Talang queenfish, Scomberoides commersonnianus, was studied in northern Australia to investigate the stock status and assess current management of the species using minimum legal lengths (MLL). Estimated von Bertalanffy growth parameters were L_∞ = 1404 mm FL, K = 0.10 year⁻¹ and t₀ = −1.21 year⁻¹. There was no significant difference in growth between sexes. Ages ranged from 1 to 11 years with age composition differing between the commercial (mainly 6–7 years) and sport fishery (mainly 2–4 years). Females matured (L₅₀) at 635 mm FL and 4–5 years. Spawning occurred between August and March when mature females were estimated to produce 259,488–2,859,935 eggs per spawning. Natural mortality (M) was estimated as 0.16–0.26 year⁻¹, while the combined fishing mortality (F_current) from commercial and sport fisheries was 0.38–0.48 year⁻¹. Yield-per-recruit analyses revealed that under current MLL limits (no MLL or 45 cm TL) and natural mortality (M = 0.16, 0.2 and 0.26 year⁻¹), F_current exceeded the reference points F_max (0.15–0.22 year⁻¹) and F_0.1 (0.10–0.15 year⁻¹), suggesting the stock may be growth overfished if the current situation remains unchanged. Although a stock–recruitment relationship is unknown, spawning stock biomass-per-recruit analysis indicates the stock may also be recruitment overfished since F_current exceeded the reference points F_25% (0.19–0.24 year⁻¹) and F_40% (0.11–0.15 year⁻¹). Increasing the MLL corresponding to L₅₀ of females (70 cm TL) will greatly improve the yield and long-term sustainability of the stock, and also enhance the sport fishery by increasing the number of larger trophy fish.     

Age and growth estimates of the sharptail mola,Masturus lanceolatus,in waters of eastern Taiwan

The sharptail mola, Masturus lanceolatus, is one of the largest teleost fishes in the world, and can be found in warm temperate and tropical regions worldwide. The increase of sharptail mola catch in the eastern Taiwan in recent years stimulated a concern that increasing exploitation of this species might lead to a decline of the stock. However, biological information of this species is very limited. Hence, this study provides the first information on age and growth of this species in the waters off eastern Taiwan based on 265 specimens (105 females and 160 males) collected from January 2003 to November 2006 at the Nanfanao and Hualien fish markets, eastern Taiwan. The relationships between whole weight (W) and standard length were expressed as: W = 9.98 × 10^?4 SL^2.45 (n = 105, p < 0.01) for females, and W = 3.33 × 10^?4 SL^2.68 (n = 160, p < 0.01) for males. Based on the MIR analysis, growth band pairs (including translucent and opaque bands) in vertebrae formed once a year and were counted up to 23 and 16 for females and males, respectively. Three growth functions, the von Bertalanffy (VBGF), Robertson, and Gompertz, were used to model the observed length at age data. The VBGF had the best fit and predicted an asymptotic length (L_∞) = 262.5 cm SL, growth coefficient (k) = 0.046 yr^?1, age at zero length (t₀) = ?3.350 yr (n = 80, p < 0.01) for females, and L_∞ = 231.0 cm SL, k = 0.059 yr^?1, t₀ = ?1.852 yr (n = 135, p < 0.01) for males. The longevities were estimated to be 105 and 82 yr based on the VBGF for females and males, respectively.     

The effects of food and the sum of effective temperature on the embryonic development of the seahorse,Hippocampus kuda Bleeker

The effect of different food (live Acetes spp., live Mysis spp., frozen Mysis spp., and mixed food of 50% live Acetes spp. and 50% frozen Mysis spp.) on gonad development of seahorses, Hippocampus kuda Bleeker, was evaluated in this experiment. The developmental durations of testes and ovary of seahorses were significantly different among the four experimental treatments. The live Acetes spp. treatment presented the shortest developmental durations to stage V, which were 87.6 ± 3.84 days and 89.2 ± 3.71 days, respectively, for ovary and testes. The frozen Mysis spp. treatment had the longest developmental durations (F_3,15 = 13.284, P < 0.05). The relationship between developmental duration of the ovary and gonad developmental stages could be formulated: Y₁ = 12.04x + 24.36 (r² = 0.9722, n = 16, P < 0.05). The gonadosomatic index (GSI) of parent seahorses among the four treatments differed significantly (F_3,15 = 18.364, P < 0.05). The standard GSI of seahorses fed live Acetes spp. was 15.64 ± 1.65%, which was the highest. Feeding live food had a significant effect on the fecundity and spawning of seahorses. The fecundity and spawning number of the live Acetes spp. treatment were 598 ± 45.49 and 552 ± 49.19 individuals, respectively, which were dramatically higher than those of frozen treatment (F_3,19 = 34.152, P < 0.05). Live food also had a similar effect on the fertilization and hatching rate during the embryonic development of seahorses (F_3,19 = 11.386, P < 0.05). Food treatment could also induce an indirect effect on survival rate of juveniles through gonadal and embryonic development of the parents (F_3,15 = 14.519, P < 0.05). In this experiment, the mortality within parent seahorses in the frozen Mysis spp. treatment was the highest (15.1 ± 6.55%), and the survival of juveniles was the highest in the live Acetes spp. treatment (90.4 ± 2.26% at 10 days). In conclusion, feeding live Acetes spp. significantly benefited the gonadal and embryonic development of H. kuda.The effect of temperature (22 °C, 24 °C, 26 °C, 28 °C, 30 °C and 32 °C) on the hatching time of H. kuda was also studied. We demonstrated that the higher the temperature, the shorter the hatching time, as well as the higher the hatching speed. The relationship between hatching time and temperature could be expressed: T = − 39.337 t + 677.75 (r² = 0.9755, n = 30, P < 0.05). In this finding, we provided the sum of effective temperature (SET) and threshold temperature of embryonic development of H. kuda (14066.9 °C h^− 1 and 13.7 °C, respectively). This new information on the effect of feeding type and culture temperature is beneficial for the commercial rearing and breeding industry of this species.     

The lack of genetic differentiation of pacu (Piaractus mesopotamicus) populations in the Upper-Paraguay Basin revealed by the mitochondrial DNA D-loop region: Implications for fishery management

Pacu (Piaractus mesopotamicus) is an important fish species for professional and sport fisheries in the Alto-Paraguay Basin, located in the central western Brazil. In this study the D-loop control region of mtDNA sequence data was used to investigate genetic variability within and among populations of pacu. A total of 99 individuals were collected in the Paraguay River and in four other main tributaries. From these, 27 different haplotypes were observed. The overall nucleotide diversity and haplotype diversity were high in all sampling sites with 0.013 ± 0.001 and 0.840 ± 0.035, respectively. Hierarchical AMOVA analysis showed that pacu populations form a single panmictic population with low Φ_ST = ?0.0012 (p = 0.486) and high gene flow among rivers. Despite high genetic variability, the total capture officially landed in the Upper-Paraguay River Basin has been decreasing steadily during the last years with indications of overexploitation. Taking into account the heterogeneity of habitats, continuous anthropogenic disturbances and lack of genetic structure, it appears that fish from these sampling sites function as a metapopulation, a framework that may be applied to long term fishery management of pacu in the Panatanal.     

Use of stochastic models to estimate the growth of the Port Jackson shark,Heterodontus portusjacksoni,off eastern Victoria,Australia

Three stochastic models were used to describe the growth of Heterodontus portusjacksoni off eastern Victoria, Australia. The models are based on a reparametrization of the von Bertalanffy growth model to take account of length-at-age heterogeneity, and incorporate random variation of the von Bertalanffy growth coefficient (k), using three different probability distribution functions (pdfs): Weibull, gamma and log-normal. They were fitted to the lengths of 179 specimens (79 females and 100 males), and associated age estimates obtained by counting growth bands in the inner trunk dentine layer of the dorsal-fin spines. The species is relatively long-lived (maximum estimated age of 35 years for females and 28 years for males) and slow growing, but has rapid growth during the early stages of life. All the models provided similar growth parameters and length-at-age quantiles. However, Kullbac?s information mean indicated that the stochastic model assuming a log-normal distribution fitted the length-at-age data better for both females (L∞ = 1337, E(k) = 0.059, t₀ = 5.294) and males (L∞ = 1125, E(k) = 0.075, t₀ = 4.944) than the models assuming other distributions. The χ² likelihood ratio test indicated that females and males grow differently.     

Effects of diet composition and ultrasound treatment on particle size distribution and carbon bioavailability in feces of rainbow trout

The effect of a high and low non-starch polysaccharide diet (HNSP and LNSP diet) and ultrasound treatment on particle size distribution and carbon bioavailability in fecal waste of rainbow trout (Oncorynchus mykiss) was studied. Feces were collected from four flow-through fish tanks, two tanks fed the HNSP diet and two the LNSP diet. The collected feces were sonicated (disintegrated) in duplicate with high-intensity (0.6 W/ml), low-frequency (f = 20 Hz) ultrasound at five different energy levels (0.6 W/ml for 0, 0.25, 1, 4, and 16 min). The particle size distribution of the treated feces samples was measured by wet sieving (1000, 500, 200, 100, 63, 36, 1.2 μm screen size) and total suspended solids (TSS) measurement. Carbon bioavailability in sonicated fecal waste samples was determined with oxygen uptake rate (OUR) tests. The results showed that: (1) feces from the HNSP diet contained significant more particulate material and bigger particles; (2) carbon bioavailability was almost three times higher in untreated LNSP feces when compared with HNSP feces; (3) almost 50% of HNSP feces could have been recovered on a microscreen of 36 μm after wet sieving, whereas it was only 10% for LNSP feces; (4) the production of small particles (1.2–36 μm), which could pass a drum filter screen and potentially accumulate in RAS, was approximately 50 g/kg feed, showing no significant differences between diets; (5) sonication increased fecal dry matter below 36 μm (p = 0.015), but it had no significant effect on the median particle size; (6) sonication increased carbon bioavailability with 7–10% for the HNSP feces (p = 0.037); (7) fecal particles withstood up to 16 min sonication at an intensity of 0.6 W/ml and a frequency of 20 Hz corresponding to specific energy input of 20,000 kJ/kg DM without major changes in particle size distribution. The results of this study indicate that the applied ultrasound treatment of fecal waste is not an effective method to increase short-term carbon bioavailability.     

Movement patterns and growth estimates of big skate (Raja binoculata) based on tag-recapture data

From 2003 through 2006, 18,180 big skate (Raja binoculata) were tagged in three regions in British Columbia, Canada: northern Hecate Strait, Queen Charlotte Sound and the west coast of Vancouver Island. To date, this is the largest tagging program conducted for skates or rays worldwide. As of December 31, 2008, 7% of the tagged fish (n = 1238) have been recaptured through the commercial fisheries. Generally, 75% of the recaptured fish were recaptured within 21 km of the tagging location. Long-range movements (up to 2340 km) were undertaken by a small percentage (1.5%) of the recaptured fish. Tagged big skate were recaptured in waters off of Oregon, Washington, throughout the Gulf of Alaska and the Bering Sea. The majority of big skate recaptured outside of Canadian waters were female (83%, n = 15), of which 80% (n = 12) were likely immature at release. Three methods of estimating growth parameters were employed and produced varying results. The Gulland and Holt method was not able to produce growth parameter estimates. The GROTAG method for combined sexes produced von Bertalanffy growth curve parameters L_∞ (294.7 cm), K (0.05) and t₀ (?1.44) that were similar to published estimates for British Columbia big skates. The von Bertalanffy growth curve parameters produced by Fabens method for combined sexes were L_∞ = 168.6 cm, K = 0.16 and t₀ = ?0.81.