Capture Depth Research Articles

Unexplained Variation in Movement by Walleye and Sauger after Catch‐and‐Release Angling Tournaments

AbstractWalleye Sander vitreus is a popular species for catch‐and‐release angling tournaments in North America, but we currently know little about the postrelease behavior of this species and the congeneric Sauger S. canadensis. We used radiotelemetry and acoustic telemetry to track Walleyes (n = 101) and Saugers (n = 19) for 7 d after release at tournaments in Saskatchewan. Our objectives were to provide a description of postrelease movements, and examine the influence of handling variables and stress scores on movement. Walleyes made highly variable movements over 7 d, and total dispersal ranged from less than 100 m to over 28 km from the release point. Path lengths—the cumulative distance between start and end points—were considerably longer than straight‐line dispersal. Walleyes made larger movements than Saugers, with average total dispersal values of 6.1 ± 6.9 km (mean ± SD) and 1.3 ± 1.8 km, respectively. Multivariate modeling revealed that species and tournament were the only important factors affecting movement. Fish size (TL), capture depth, distance transported, and time spent in a live well were not consistently important predictors of postrelease movement. Walleyes and Saugers moved much smaller distances when they had poor outcomes for the reflex action mortality predictor (RAMP) test, but RAMP scores in general did not explain a significant proportion of the variance in any fish movement metric. Swim scores at the time of release, an alternative metric of stress, also did not explain a significant proportion of variance in fish movement. Our results show intriguing variance in the behavioral response of individual Walleyes and Saugers to catch and release at tournaments, but do not identify causal factors.

Spatial variability of lake trout diets in Lakes Huron and Michigan revealed by stomach content and fatty acid profiles

Despite long-term efforts to restore lake trout (Salvelinus namaycush) populations in the Great Lakes, they continue to experience insufficient recruitment and rely on hatchery programs to sustain stocks. As lake trout reproductive success has been linked to diets, spatial heterogeneity in diet compositions is of interest. To assess spatial components of adult lake trout diets, we analyzed stomach contents and fatty acid profiles of dorsal muscle collected throughout Lake Michigan and along Lake Huron’s Michigan shoreline. Lake trout from Lake Huron were generally larger in both length and mass than those from Lake Michigan. However, lake trout from Lake Michigan varied more in size based on depth of capture with smaller fish being caught more in deeper set nets. Fatty acids and stomach contents indicated that alewife (Alosa pseudoharengus) were consumed more in western Lake Michigan in contrast with round goby (Neogobius melanostomus) along the eastern shoreline. Conversely, in Lake Huron, lake trout primarily consumed rainbow smelt (Osmerus mordax). These results indicate that diet compositions of lake trout populations are relatively plastic and offer new insights into within-basin heterogeneity of Great Lakes food webs.

Deep-water bony fishes collected by the B/O Miguel Oliver on the shelf edge of Pacific Central America: an annotated, illustrated and DNA-barcoded checklist.

An annotated and photographically illustrated checklist with DNA barcodes of the species of bony fishes collected during a month-long research cruise of the Spanish Research vessel B/O Miguel Oliver is presented. The vessel made trawls on the continental shelf of the Pacific coast of Central America, in November-December 2010, at depths of 108-1625 m. This list, based on 707 specimens (of a total of 876 specimens collected during the whole expedition), includes 129 species belonging to 15 orders, 61 families, and 97 genera. New information is presented on the geographical distributions of more than a third of those species, with 29 species (22.4%) representing new records from Central American waters and 17 species (13.2%) having expanded latitudinal ranges. Data on capture depths demonstrate increased depth ranges due to new minimum and/or maximum known depths for 31 species, i.e. 24% of those captured. Tissue samples from frozen specimens were used to obtain DNA barcodes of 682 (96.5%) individuals belonging to 118 species (91.4% of those recorded here), which have been made publically available in Genbank. Those data include barcodes for 84 species (65.1% of the total collected, and 77.1% of those for which barcodes were obtained) and 30 genera (30.9% of those collected) for which no species barcodes have been previously published. Barcodes of 54 species represent the first genetic sequences of any type published for those species. The abundance of new data indicate that there is still much to learn about the composition and geographical and depth distributions of the fish fauna of the shelf edge and continental slope of this region.

Thermoconformity strategy in the freshwater turtle Hydromedusa tectifera (Testudines, Chelidae) in its southern distribution area

Ectotherm species are not capable of generating metabolic heat; therefore, they present different strategies for regulating their body temperatures, ranging from a precise degree of thermoregulation to a passive thermoconformity with ambient temperatures. In reptiles, aerial basking is the most common mechanism for gaining heat. However, among aquatic reptiles, such as freshwater turtles, aquatic basking is also frequent. Hydromedusa tectifera is a turtle of exclusively aquatic and nocturnal habits widely distributed in South America. We studied the relationship between body temperature (Tb) of H. tectifera and its habitat, and explored the effects of sex, life stage and body size and mass on Tb. Fieldwork was conducted in two streams of a mountain area of central Argentina. We recorded cloacal temperature, size and mass of 84 turtles. We also determined individuals’ sex and life stage (adult/juvenile). Regarding ambient temperatures, we measured water temperature on the surface (Tsurf) and at depth of turtle capture (Tdepth) and air temperature. Mean Tb was 18.58°C (Min = 10.20°C; Max = 25.70°C). Tsurf and Tdepth were highly correlated. Multi-model analysis using Akaike criterion indicated that Tb was strongly associated with water temperature, whereas air temperature and body size and mass did not show a significant effect. There was also no effect of turtle sex or life stage on Tb. Our results indicate that H. tectifera is a thermoconformer and eurythermal species. A nocturnal pattern of activity and a fully aquatic lifestyle are suggested as determinant factors.

Metabolic enzyme activities of abyssal and hadal fishes: pressure effects and a re-evaluation of depth-related changes

Metabolic enzyme activities of muscle tissue have been useful and widely-applied indicators of whole animal metabolic capacity, particularly in inaccessible systems such as the deep sea. Previous studies have been conducted at atmospheric pressure, regardless of organism habitat depth. However, maximum reaction rates of some of these enzymes are pressure dependent, complicating the use of metabolic enzyme activities as proxies of metabolic rates. Here, we show pressure-related rate changes in lactate and malate dehydrogenase (LDH, MDH) and pyruvate kinase (PK) in six fish species (2 hadal, 2 abyssal, 2 shallow). LDH maximal reaction rates decreased with pressure for the two shallow species, but, in contrast to previous findings, it increased for the four deep species, suggesting evolutionary changes in LDH reaction volumes. MDH maximal reaction rates increased with pressure in all species (up to 51±10% at 60MPa), including the tide pool snailfish, Liparis florae (activity increase at 60MPa 44±9%), suggesting an inherent negative volume change of the reaction. PK was inhibited by pressure in all species tested, including the hadal liparids (up to 34±3% at 60MPa), suggesting a positive volume change during the reaction. The addition of 400mM TMAO counteracted this inhibition at both 0.5 and 2.0mM ADP concentrations for the hadal liparid, Notoliparis kermadecensis. We revisit depth-related trends in metabolic enzyme activities according to these pressure-related rate changes and new data from seven abyssal and hadal species from the Kermadec and Mariana trenches. Results show that, with abyssal and hadal species, pressure-related rate changes are another variable to be considered in the use of enzyme activities as proxies for metabolic rate, in addition to factors such as temperature and body mass. Intraspecific increases in tricarboxylic acid cycle enzymes with depth of capture, independent of body mass, in two hadal snailfishes suggest improved nutritional condition for individuals deeper in the hadal zone, likely related to food availability. These new data inform the discussion of factors controlling metabolism in the deep sea, including the visual interactions hypothesis and extend published trends to the planet's deepest-living fishes.

Recreational Postrelease Mortality of Lake Trout in Lakes Superior and Huron

AbstractThe effectiveness of fishing regulations that result in the release of some angler‐caught fish depends on accurate knowledge of the postrelease mortality of those individuals. In the Laurentian Great Lakes, Lake TroutSalvelinus namaycushare a major component of recreational fisheries; across large regions of the lakes, they are managed with length limit and daily quota regulations assuming a 15% postrelease mortality rate. Due to concerns regarding the accuracy of that rate, we conducted a tagging study to estimate Lake Trout postrelease mortality in Lakes Superior and Huron, and we examined environmental and fishing factors that influenced the return rates of tagged fish. The basic study design was to compare tag return rates between two groups: (1) a treatment group comprising fish that were caught and released by anglers; and (2) a control group comprising fish that were caught via trap net and released. Tag return rates for the angler‐caught group were evaluated in relation to depth of capture, surface temperature at release (ST), fishing method, anatomical hook site, play time, handling time, and barotrauma. Tag return rates for angler‐caught fish declined significantly with increasing ST; the other factors’ effects on tag return rates were generally small. For Lake Superior, model‐averaged (Akaike's information criterion) postrelease mortality estimates incorporating ST were 15.0% (SE = 5.6%) at STs less than 10°C, 42.6% (SE = 3.0%) at STs of 10–16°C, and 43.3% (SE = 3.6%) at STs greater than 16°C. Model‐averaged estimates for Lake Huron were 52.5% (SE = 26.8%) at STs less than 10°C, 45.2% (SE = 14.0%) at STs of 10–16°C, and 76.4% (SE = 5.4%) at STs greater than 16°C. Based on these findings, alternative fishery management regulations that limit recreational catch‐and‐release angling of Lake Trout in the Great Lakes may be prudent. Current management policies based on an assumed 15% postrelease mortality are likely underestimating the total numbers of Lake Trout that are removed by recreational anglers.Received January 26, 2017; accepted April 29, 2017 Published online June 26, 2017

Venting and Descending Provide Equivocal Benefits for Catch‐and‐Release Survival: Study Design Influences Effectiveness More than Barotrauma Relief Method

AbstractDescending fish to depths of neutral buoyancy is a promising, less‐invasive alternative to swim bladder venting for relieving barotrauma and reducing mortality in sport fish. However, we lack a broad perspective on the relative benefits of these two approaches. We reviewed the most up‐to‐date literature to evaluate the effectiveness of venting compared to descending treatments. Mean relative risk (RR) based on 76 published comparisons (51 marine, 25 freshwater; 18 genera, 28 species) showed that venting (2.0 ± 4.7 [mean ± SD]) and descending (1.6 ± 1.4) both had positive effects on survival (RR ≥ 1.1). However, RR was generally small and statistically indistinguishable between treatments, providing no strong support for the use of one method over the other. Modeling of factors affecting RR showed that the study design variable “assessment method” was the only important factor affecting RR, having a larger influence on survival than habitat, capture depth, or treatment type (venting versus descending). Biotelemetry and ex situ methods produced significantly higher estimates of RR than other assessments. Our review suggests that the two major approaches to barotrauma relief do not differentially influence survival outcomes and that study design may be an important source of bias. Consequently, we recommend that managers consider barotrauma relief options carefully on a case‐by‐case basis, and we encourage additional research on sublethal endpoints in addition to mortality.Received November 29, 2016; accepted March 9, 2017 Published online May 4, 2017

Estimating Heart Rate and Rhythm via 3D Motion Tracking in Depth Video

Low-cost depth sensors, such as Microsoft Kinect, have potential for noncontact health monitoring that is robust to ambient lighting conditions. However, captured depth images typically suffer from high acquisition noise, and hence, processing them to estimate biometrics is difficult. In this paper, we propose to capture depth video of a human subject using Kinect 2.0 to estimate his/her heart rate and rhythm; as blood is pumped from the heart to circulate through the head, tiny oscillatory head motion due to Newtonian mechanics can be detected for periodicity analysis. Specifically, we first restore a captured depth video via a joint bit-depth enhancement/denoising procedure, using a graph-signal smoothness prior for regularization. Second, we track an automatically detected head region throughout the depth video to deduce 3D motion vectors. The detected vectors are fed back to the depth restoration module in a loop to ensure that the motion information in two modules is consistent, improving performance of both restoration and motion tracking. Third, the computed 3D motion vectors are projected onto its principal component for 1D signal analysis, composed of trend removal, bandpass filtering, and wavelet-based motion denoising. Finally, the heart rate is estimated via Welch power spectrum analysis, and the heart rhythm is computed via peak detection. Experimental results show accurate estimation of the heart rate and rhythm using our proposed algorithm as compared to rate and rhythm estimated by a portable oximeter.

Reproductive Status and Blood Plasma Indicators of Sex and Gonad Maturation Status for Yelloweye Rockfish Following Barotrauma and Recompression Events

AbstractDiscard mortality of rockfishes Sebastes spp. is a management concern along the West Coast of North America. Although many rockfish species survive after barotrauma and forced recompression, it is unclear whether these mechanisms affect reproductive success. We examined whether (1) Yelloweye Rockfish S. ruberrimus in Prince William Sound, Alaska, could reproduce up to 2 years after one or more barotrauma and recompression events; and (2) blood plasma indicators (i.e., vitellogenin [VTG] and calcium [Ca2+]) could be used to identify sex and gonad maturation stage. In 2010, we captured and examined Yelloweye Rockfish that had been tagged in 2008 and 2009, and all mature females were gravid or spent. The most common barotrauma sign was esophageal eversion, with females and males exhibiting this injury 50% and 90% of the time, respectively. All other injuries, except swim bladder ruptures and tears, occurred at low frequencies and (with the exception of esophageal eversion) increased in frequency with capture depth. Mean plasma VTG concentrations for females were greater than those for males; with the exception of stage‐0 females, there were no differences in VTG among female gestation stages. Mean plasma Ca2+ concentrations for stage‐2 females differed from those of males, stage‐0 recruits, and immature fish. However, there was no difference in mean Ca2+ among female reproductive stages. These results indicate that reproduction of Yelloweye Rockfish is not affected after barotrauma and recompression events and that blood plasma measures show variable success as indicators of sex and female reproductive status.Received March 16, 2016; accepted August 12, 2016 Published online September 30, 2016

Delayed effects of capture-induced barotrauma on physical condition and behavioral competency of recompressed yelloweye rockfish, Sebastes ruberrimus

Rebuilding of some U.S. West Coast rockfish (Sebastes spp.) stocks relies heavily on mandatory fishery discard, however the long-term condition of discarded fish experiencing capture-related barotrauma is unknown. We conducted two studies designed to evaluate delayed mortality, physical condition, and behavioral competency of yelloweye rockfish, Sebastes ruberrimus, experiencing barotrauma during capture followed by recompression (assisted return to depth of capture). First, we used sea-cage and laboratory holding to evaluate fish condition at 2, 15, and 30days post-capture from 140 to 150m depth. All external barotrauma signs resolved following 2days of recompression, but fish that survived (10/12) had compromised buoyancy regulation, swim bladder injuries, and coelomic and visceral hemorrhages at both 15 and 30days post-capture. For the second study, we used a video-equipped sea-cage to observe fish behavior for one hour following capture and return to the sea floor. Trials were conducted with 24 fish captured from 54 to 199m water depth. All fish survived, but 50% of fish from the deepest depth ranges showed impairment in their ability to vertically orient (P<0.01). Most (75%) deep-captured fish did not exhibit “vision-dependent” behavior (P<0.001) and appeared unable to visually discern the difference between an opaque barrier and unobstructed or transparent components of the cage. These studies indicate physical injuries and behavioral impairment may compromise yelloweye rockfish in the hours and weeks following discard, even with recompression. Our results reiterate the importance of avoiding fishing contact with species under stock rebuilding plans, especially in deep water, and that spatially-managed rockfish conservation areas remain closed to fishing.

Modelling the Diel Vertical Movement of Swordfish (Xiphias gladius Linnaeus, 1758) Based on Temperature and Depth Recorder Data

Understanding the vertical distribution of large pelagic fish, swordfish in particular, could improve our knowledge on its fisheries strategy, management and resource conservation. However the methods often require expensive tools and resources, which probably most scientists from the development countries couldn’t afford. Thus developing model on the diel vertical movement behavior of swordfish using number of hook between float (HBF) and complete-set temperature and depth recorder (TDR) data could be an alternative. In general context, capture depth distributions are a good indicator of the natural depth distribution of the fish if the entire depth range of the species is targeted by longline gear. The proposed sinusoidal model suggested that swordfish showed a diel pattern in depth distribution, marked by remained in the surface and mixed layer waters at night and dived into deeper waters during the day. Keywords: swordfish, behavior, HBF, TDR, sinusoidal model

Changes in depth occupied by Great Lakes lake whitefish populations and the influence of survey design

Understanding fish habitat use is important in determining conditions that ultimately affect fish energetics, growth and reproduction. Great Lakes lake whitefish (Coregonus clupeaformis) have demonstrated dramatic changes in growth and life history traits since the appearance of dreissenid mussels in the Great Lakes, but the role of habitat occupancy in driving these changes is poorly understood. To better understand temporal changes in lake whitefish depth of capture (Dw), we compiled a database of fishery-independent surveys representing multiple populations across all five Laurentian Great Lakes. By demonstrating the importance of survey design in estimating Dw, we describe a novel method for detecting survey-based bias in Dw and removing potentially biased data. Using unbiased Dw estimates, we show clear differences in the pattern and timing of changes in lake whitefish Dw between our reference sites (Lake Superior) and those that have experienced significant benthic food web changes (lakes Michigan, Huron, Erie and Ontario). Lake whitefish Dw in Lake Superior tended to gradually shift to shallower waters, but changed rapidly in other locations coincident with dreissenid establishment and declines in Diporeia densities. Almost all lake whitefish populations that were exposed to dreissenids demonstrated deeper Dw following benthic food web change, though a subset of these populations subsequently shifted to more shallow depths. In some cases in lakes Huron and Ontario, shifts towards more shallow Dw are occurring well after documented Diporeia collapse, suggesting the role of other drivers such as habitat availability or reliance on alternative prey sources.

Ichthyoplankton distribution and abundance in relation to nearshore dissolved oxygen levels and other environmental variables within the Northern California Current System

Nearshore hypoxia along the coast of Oregon and Washington is a seasonal phenomenon that has generated concern among scientists studying this temperate upwelling ecosystem. These waters are affected by coastal upwelling-induced hypoxia mainly during late summer and fall, but the effects of low oxygen levels on fish and invertebrate communities, particularly during the early-life history stages, are poorly known. We investigated the effects of hypoxia and other variables on the species composition, density, vertical and horizontal distribution of fish larvae along the Oregon and Washington coasts during the summers of 2008, 2009 and 2010. Bottom-dissolved oxygen (DO) values ranged from 0.49 to 4.79 mL L−1, but the overall water column DO values were only moderately hypoxic during the 3 yr of sampling compared with recent extreme years. In this study, DO was found to be an environmental parameter affecting the species composition, but other variables such as season, year and depth of capture were also important. Although the overall density of fish larvae increased with increasing bottom-DO values, the effect on individual species density was limited. Slender sole (Lyopsetta exilis) and sand sole (Psettichthys melanostictus) were the only species to have a weak trend of density with DO, but both showed negative relationships and neither relationship was significant. Our results indicate that larval fish spatial distribution was only moderately affected within the range of observed oxygen values, but low DO may be an important factor under intense hypoxic conditions.

A cage release method to improve fish tagging studies

The return and survival of tagged fish to their depth of capture has proved difficult due to barotrauma and predation in previous telemetry studies. Tagging stress can slow and disorient the fish upon release, and reduce the ability to return to depth, relocate their home habitat site, and evade predators. To reduce these initial tag and release artifacts we designed and tested a remotely opening cage for use with reef fish in the northern Gulf of Mexico. Our objectives were to quickly return transmitter tagged fish to depth (20–30m) in close proximity (<10m) to their capture site, and to increase survival by providing predator protection during an initial recovery period. This cage release method proved successful for both red snapper (Lutjanus campechanus; n=62 out of 71, 87%) and all gray triggerfish (Balistes capriscus; n=24) that were tagged and released on artificial reefs. All tagged fish were released from November 2012 to September 2014, no initial tag induced mortalities were observed, and after tagging fish were successfully tracked for extended periods (for the entire 2 year study period).

Dive to survive: effects of capture depth on barotrauma and post-release survival of Atlantic cod (Gadus morhua) in recreational fisheries

Abstract Atlantic cod (Gadus morhua) caught in recreational fisheries are commonly released, often with barotrauma after rapid decompression. Mouth-hooked, non-bleeding cod kept in a floating net pen showed mortalities ≥40% when angled from &amp;gt;50 m depth, likely because of cumulative stress from ongoing barotrauma and exposure to warm surface water. In a natural setting, however, cod have the opportunity to descend after release and are not restricted to the surface. In a follow-up study, 97.8% of similarly selected cod managed to dive following immediate release, whereas 2.2% were floaters. No mortality was observed for divers kept in cages, which were lowered to capture depth for 72 h. While the floaters would likely have died in a natural setting, no mortality was observed when they were recompressed and kept at capture depth for 72 h. The occurrence of swim bladder ruptures, swollen coelomic cavities, venous gas embolisms, and gas release around the anus was significantly influenced by capture depth (range 0–90 m). A supplementary radiology study showed inflated swim bladders in 87% of the cod after 72 h, and most barotrauma signs had disappeared after 1 month. This study encourages investigation of survival potential for physoclistous species when high mortalities are assumed but undocumented. Matching natural post-release and containment environment is essential in the experimental setup, as failure to do so may bias survival estimates, particularly when a thermocline is present. Assuming minimal predation, short-term mortality of cod experiencing barotrauma is negligible if cod submerge quickly by themselves and are otherwise not substantially injured. Survival of floaters may be increased by forced recompression to capture depth. Sublethal and long-term impacts of barotrauma remain to be studied. To ensure that cod have sufficient energy to submerge, anglers are encouraged to avoid fighting the fish to exhaustion and to minimize handling before release.

Trophic structure and food resources of epipelagic and mesopelagic fishes in the North Pacific Subtropical Gyre ecosystem inferred from nitrogen isotopic compositions

AbstractWe used bulk tissue δ13C and δ15N values and δ15N values of individual amino acids (AA) to characterize the trophic structure of a pelagic fish assemblage from the North Pacific Subtropical Gyre (NPSG) ecosystem. We focus on energy flow between fishes inhabiting distinct epipelagic, mesopelagic, and upper bathypelagic habitats and on predatory fish foraging across and within these depth habitats. Trophic positions (TPs) estimated from a combination of trophic and source AA δ15N values (TPTr‐Src) spanned a narrow range of 0.7 TP for 10 species of large fishes, including tunas, billfishes, and gempylids (TPTr‐Src 4.3‐5.0). Similarly, 13 species of small micronekton fishes encompassed a range of 1.2 TP (TPTr‐Src 2.6‐3.8). The δ15N values of three source AAs were found to increase with increasing depth of capture across the 13 micronekton fish species (δ15NPhe range = 6.6‰; δ15NGly range = 13.4‰; δ15NSer range = 13.6‰), indicating that some species from epipelagic, mesopelagic, and upper bathypelagic communities access distinct food resources, such as suspended particles. These isotopic depth trends are consistent with previous observations in particulate organic matter and zooplankton from the NPSG, providing new evidence that large pelagic and micronekton fishes access a food web fueled by particles formed in surface waters but that are highly modified by microbes as they slowly settle to remote depths. On the contrary, no significant relationships between the δ15N values of source AAs and habitat depth were observed in the large predator fish group, of which many species move and forage across large depth gradients.

Angling-induced barotrauma in snapper Chrysophrys auratus: are there consequences for reproduction?

In response to concerns regarding the potential for sub-lethal impacts of barotrauma on reproductively active Chrysophrys auratus during catch and release, 90 males and 90 females representing five reproductive stages (immature or resting-28%, developing-8%, developed-7%, ripe or spawning-23% and spent-34%) were angled from 8–70 m and macroscopically assessed (on-board and then in a laboratory). Irrespective of sex, all fish exhibited various clinical signs of barotrauma, including a prolapsed cloaca (60% of fish); gastric herniation (46%); ruptured swim bladder (73%); organ displacement (48%); and kidney (3%), liver (73%) and coloemic-cavity haemorrhaging (33%);with the frequency of nearly all positively associated with capture depth. Reproductive stage was also an important barotrauma predictor (reflecting related morphological changes) with a general trend towards spent fish least likely to incur the various clinical signs—especially for a prolapsed cloaca (also common among immature or resting fish and significantly affected by food in the digestive tract) and a ruptured swim bladder (common among ripe or spawning fish). The only macroscopically visible gonad damage was haemorrhaging, which was least common among immature or resting and spent fish and, irrespective of reproductive stage, temporally reduced in frequency, and more quickly among males than females. While further research is required to accurately describe the effects of angling at each stage of the reproductive cycle and the physiological consequences of barotrauma on the gonads of C. auratus, given the observed influences of reproductive stage and depth on barotrauma found in this study, any adverse effects might be partially managed by regulating either temporal or spatial fishing effort.

Variation in whole-, landed- and trimmed-carcass and fin-weight ratios for various sharks captured on demersal set-lines off eastern Australia

Sharks are important apex predators in marine systems but many populations have experienced large declines, which has resulted in adverse effects on marine food webs. Sharks are also economically important, as their fins are valued in Asian markets. In response to concerns about declining shark populations, a number of nations, including Australia, have developed national plans of action for their conservation and management. As part of New South Wales’ (NSW) efforts to understand the characteristics of their shark fishery, data were collected on the depth of capture, species, sex, body length and weight, fin weight, and reproductive status of individuals caught in the NSW commercial ‘large shark’ demersal set-line fishery. We created models of the relationship between fin to body weight and wastage (discarded or low value portions of the carcass) and compared the ratios of whole, landed, trimmed, and fin weight to determine the relationship between fin weight and wastage to length by species. Our results indicate that length, sex, and the interactions between length with species and sex account for differences in the relative fin weight of sharks; whereas species, length, and their interaction account for differences in the proportion of a shark carcass that is wasted. The data reveal that catching smaller sharks will increase relative fin weight and decrease wastage. Given these results, we recommend that managers consider weight ratio data information in their decision making to promote a sustainable and profitable shark fishery.

At-vessel mortality and blood biochemical status of elasmobranchs caught in an Australian commercial longline fishery

This study investigates mortality of sharks in a commercial longline fishery in Australia. To examine the rate and biological, environmental and technological factors contributing to at-vessel mortality, four setlines with 120 gangions possessing ‘hook timers’ were deployed daily (for 7h and 14h) using conventional gears from two commercial fishing vessels during 2013. A total of 689 animals across 22 species and including 18 elasmobranchs were landed. For the five species (Carcharhinus spp.), and one genus (Sphyrna spp) where there were sufficient numbers for analysis, generalised linear mixed models showed that species and the elapsed time spent on the line after hooking were the strongest predictors of at-vessel mortality, with spinner (Carcharhinus brevipinna), blacktip (C. limbatus) and hammerhead (Sphyrna spp) sharks exhibiting the highest death rates. The variables which best explained mortality, included: (i) sex of the caught sharks, and the interaction between species with (ii) capture depth, and (iii) the elapsed time spent on the line after hooking. For the subset of dusky (C. obscurus) and sandbar (C. plumbeus) sharks examined for physiological status at the point of capture, very few of the 13 chosen blood analytes varied significantly. Given the observed high mortality rates and stress associated with the time spent on the line after capture, operational changes to reduce these adverse impacts should be considered. Even simple changes such as shorter soak times could considerably mitigate these impacts.

Ecomorphological Diversity of Lake Trout at Isle Royale, Lake Superior

AbstractFour Lake TroutSalvelinus namaycushmorphs were identified from Isle Royale, Lake Superior; the morphs differed in shape, traits linked to feeding and locomotion, buoyancy, and physical habitat use. Lean, humper, and siscowet Lake Trout generally conformed to previous descriptions, and we report, for the first time, quantitative evidence of a fourth morph, previously described anecdotally as the “redfin.” Jackknife classification of individuals to morphs based on body shape were 94% correct. High variation within and low variation among morphs led to moderately low percent agreement among visual identifications and high uncertainty in Bayesian model groupings of morphs. Eight linear measures of phenotypic traits linked to feeding (i.e., head and eyes) and locomotion (i.e., fin lengths and caudal peduncle shape) varied among morphs, consistent with specialized adaptations for trophic and physical resource use. Habitat differed among morphs with leans being most abundant in the 0–50‐m depth stratum and siscowets most abundant in two deeper strata (50–100 and 100–150 m). Differences in capture depth and percent buoyancy reflected physical habitat and known trophic resource partitioning among morphs. While the historical fingerprint of morphological and ecological diversity in Lake Superior Lake Trout persists, it is unknown whether the contemporary low level of differentiation is due to ecological release without subsequent reorganization or to a complete breakdown of differentiation.Received July 11, 2013; accepted February 7, 2014