Pelagic Longline Fisheries Research Articles

Effects of Small (13/0) Circle Hooks on Loggerhead Sea Turtle Bycatch in a Small-Scale, Italian Pelagic Longline Fishery

Incidental catches by pelagic longline fisheries are recognized as serious threats to the loggerhead sea turtle, Caretta caretta (linnaeus, 1758). In the present study, we assessed the effects of small (13/0) circle hooks on the catches of C. caretta in a small-scale, pelagic longline fishery off the southern coast of ionian calabria (southern italy). Experiments were conducted on a commercial fishing vessel using circle hooks (mustad 13/0, n = 2320) alternated with J-hooks (mustad no. 4, n = 2322) along 13 longline sets. The mean catch per unit of effort (cpuE) of the target species Thunnus thynnus (linnaeus, 1758) (n = 30) per fishing set and its mean body size did not differ significantly between the two hook types. No significant differences emerged in the sea turtle cpuE for each hook type; however, there was a significant reduction in mean body size with circle hooks due to a decrease in the catch rate of large juvenile loggerhead turtles. Although more data are necessary to obtain a comprehensive picture, the widespread adoption of 13/0 circle hooks has the potential for benefitting large juveniles and nesting adult sea turtles. Our data also suggest that adoption of 13/0 circle hooks would not adversely impact the economic viability of the fishery.

The Effect of Circle Hooks on Shark Catchability and At-Vessel Mortality Rates in Longlines Fisheries

Circle hooks have gained recent attention as a cost-effective bycatch mitigation tool in pelagic longline fisheries, particularly for marine turtles. Over the last few years, a growing number of studies have investigated the use of circle hooks and their effects on other species, including elasmobranchs. To elucidate the potential value of circle hook use as a tool for shark conservation and management in pelagic longline fisheries, we conducted a quantitative review of all available studies to date. We compiled 15 published and eight gray literature studies and where possible used random effects meta-analysis and analysis of covariance to test the effects of circle hooks on catchability and at-vessel mortality rates. Overall, results suggest that using circle hooks on pelagic longlines do not have a major effect on shark catch rates, but do reduce at-vessel mortality compared to J-hooks. Thus circle hooks should be seen as one potential tool to help reduce bycatch mortality of sharks in longline fisheries. However, the high level of heterogeneity found between studies highlights the need for shark-specific controlled experiments to provide more definitive results.

Hooking Survival of Fishes Captured by the United States Atlantic Pelagic Longline Fishery: Impact of the 2004 Circle Hook Rule

We examine the impact on pelagic fish hooking survival rates (defined as the proportion of fish alive upon gear retrieval) of the rapid switch from J-hooks to circle hooks that was required of the us pelagic longline fishery operating in the atlantic ocean and gulf of mexico after august 2004. Our focus was on 12 fish taxa that are commonly caught as bycatch or retained for the market, and for which individual disposition (live or dead) information was available from 1992 to 2010. To test the hypothesis of no change in survival before vs after the circle hook rule went into effect, we utilized a repeated measures logistic regression approach which accounted for variation in several operational, environmental, and biological covariates, including bait, fishery target, fishing zone, soak duration, water temperature, maximum fishing depth, and fish size (length). For white marlin and albacore, results were mixed, with both increases and decreases in hooking survival varying by fishing zone. For blue shark and lancetfish, no significant differences in hooking survival were detected between the pre- and post-circle hook rule time periods. However, for the remaining eight taxa (swordfish, yellowfin tuna, dolphinfish, bigeye tuna, escolar, silky shark, blue marlin, and sailfish), significant increases in survival were evident. Our results are generally consistent with previous experimental and fishery observer longline studies which suggested circle hook use has the potential to increase hooking survival. Results imply that the 2004 circle hook rule has provided increased opportunities for: (1) live release for several bycatch species; and (2) improved quality (and perhaps prices) of targeted and incidentally-caught taxa that are retained for the market.

Can Circle Hook Offset Combined with Baiting Technique Affect Catch and Bycatch in Pelagic Longline Fisheries?

Circle hooks have become a standard requirement in many commercial longline fisheries in the united states, and are used increasingly worldwide. Circle hooks, when compared to J-hooks, are thought to reduce bycatch without significantly decreasing (and possibly increasing) catch of most target species. Circle hook offset and baiting technique are also thought to influence bycatch and mortality of species of concern, such as sea turtles and billfishes. We compared non-offset circle hooks to those with a 10° offset and single or threaded baiting techniques in the united states atlantic and gulf of mexico pelagic longline fishery. Offset and/or baiting techniques were compared within sets targeting one of three species independently: swordfish, Xiphias gladius linnaeus, 1758, yellowfin tuna, Thunnus albacares (bonnaterre, 1788), and bigeye tuna, Thunnus obesus (lowe, 1839). Most comparisons of catch and bycatch did not differ between gears or techniques. In swordfish-directed sets, we found a 46% decline in catch of atlantic sailfish when using 18/0 non-offset circle hooks single baited with mackerel compared to 18/0 10° offset circle hooks with threaded mackerel. In yellowfin tuna sets, single baiting significantly decreased target catch by 22% and escolar catch by 28%, compared to threaded baiting. We detected no significant effect of any of the offset or baiting treatments on the bycatch of sea turtles and most other species of concern due to the rarity of capture events. We conclude, in part, that bycatch mitigation research in other fisheries with larger detrimental population level impacts to species of concern may potentially yield greater conservation benefits.

Circle Hook Performance in the Uruguayan Pelagic Longline Fishery

Circle hooks have been promoted as an alternative to traditional J-hooks in pelagic longline fisheries to minimize bycatch mortality and injury to sea turtles and other marine wildlife. We evaluated the effect of hook type (circle hook vs J-hook) on the catch and length composition of target and non-target species in the Uruguayan pelagic longline fishery, for both American- and Spanish-style longlines. The sample unit used for comparing catches was two consecutive sections of the longline, each with a different hook type. For the American-style longline 39,822 hooks were deployed in 108 paired sections, and for the Spanish-style 45,142 hooks were deployed in 238 paired sections. The catch of albacore tuna, Thunnus alalunga (Bonnaterre, 1788), was higher with circle hooks with both gears. The catch of shortfin mako shark, Isurus oxyrinchus (Rafinesque, 1810), also increased with the use of circle hooks, but only with the American-style longline. A decrease was observed in the catch of pelagic stingray, Pteroplatytrygon violacea (Bonaparte, 1832), with both gears, though it was significant only with the Spanish-style longline. The performance of circle hooks for other target species, such as swordfish, Xiphias gladius (Linnaeus, 1758), and sharks, and for bycatch species including sea turtles and seabirds remains unclear and requires further research.

Perspectives on the Morphological Elements of Circle Hooks and Their Performance in Pelagic Longline Fisheries

Use of circle hooks is regarded as an effective method to reduce incidental mortality of non-targeted species (e.g., sea turtles) in longline fisheries. Currently, various types of circle hook are produced and distributed commercially. Many researchers worldwide have examined the effect of circle hooks on hooking location, catch rate, and/or mortality for various species, using different types of hooks of various shapes and sizes. However, much work remains to be done to quantify the effects of circle hooks on catch and mortality rates of both target and non-target species. Consideration of practical utility is also important to facilitate wider application of circle hooks in commercial fisheries. Here we focus on some elements of circle hook morphology, i.e., hook width, offset, and incurved point angle, and discuss their potential effects on hook function (i.e., hooking location, catch rate) and practical utility. Further empirical circle hook studies are required to verify the effects discussed here.

Incorporating Circle Hooks Into Atlantic Pelagic Fisheries: Case Studies from the Commercial Tuna/Swordfish Longline and Recreational Billfish Fisheries

An emerging body of literature has demonstrated the benefits of the use of circle hooks relative to standard J-hooks in commercial and recreational fisheries. In the pelagic longline fishery for tunas (Thunnus spp.) and swordfish (Xiphias gladius Linnaeus, 1758), the use of circle hooks has resulted in greater catch rates of some target species, lower catch rates of some bycatch species, and a higher percentage of many target and bycatch species alive at the time of haulback (gear retrieval). However, a lack of agreement among results of studies conducted in different fisheries and areas, using different baits and rigging techniques, and with different styles and sizes of circle hooks has hindered the adoption of this terminal tackle as a management measure at the international level. Nevertheless, some countries have mandated the use of circle hooks in pelagic longline fisheries to protect bycatch species, and some individual fishers have incorporated circle hooks because they appear to maximize individual profit. In the recreational fishery for billfishes (family Istiophoridae), which is primarily a catch-and-release fishery in the United States, studies have demonstrated that circle hooks result in higher rates of external hooking and post-release survival than standard J-hooks. The use of circle hooks in billfish fisheries has been promoted by the sportfishing industry and is currently required by some nations; however, partnerships promoting active outreach and education with stakeholders in both commercial and recreational fisheries are critical to maximize the use and conservation benefit of this technology.

Effects of 16/0 Circle Hooks on Pelagic Fish Catches in Three South Pacific Albacore Longline Fisheries

The present study tested the effects of using large 16/0 circle hooks on catch rates in three pelagic longline fisheries in the south pacific ocean. large (16/0) circle hooks were tested against a variety of smaller hooks already in use by longline vessels in american samoa, cook islands, and new caledonia. The majority of these fleets use a mix of hook sizes, including circle hooks that are smaller than a 16/0 circle hook. Vessels alternated hooks throughout every set, maintaining a 1:1 ratio of 16/0 circle hooks to their existing hooks. information on catch by hook size, fish lengths, and condition at gear retrieval was collected. in total, 4912 fishes of 33 species were observed on 145,982 hooks from 67 sets. in the cook islands fishery, there was no significant difference in catch by hook type for two main target species, but there was an increase in catchability for swordfish, Xiphias gladius (linnaeus, 1758). in the new caledonia fishery, there was no significant difference in catch by hook size for any species. in the american samoa fishery, 16/0 circle hooks did not significantly affect the catch of albacore, Thunnus alalunga (bonnaterre, 1788), but did significantly reduce the catch of skipjack tuna, Katsuwonus pelamis (linnaeus, 1758), dolphinfish, Coryphaena hippurus (linnaeus, 1758), and wahoo, Acanthocybium solandri (cuvier, 1832). for all locations, catch rates on 16/0 circle hooks were nominally lower, but not always significant for smaller pelagic species.

Evaluation of Hook and Bait Type on the Catch Rates in the Western North Atlantic Ocean Pelagic Longline Fishery

Research was conducted in 2002 and 2003 by noaa's national Marine fisheries service, southeast fisheries science center, to investigate changes in hook design and bait type to reduce the bycatch of sea turtles on pelagic longlines in the western north atlantic ocean. The effectiveness of 18/0-20/0 circle hooks and 10/0 Japanese tuna hooks with squid (Illex spp.) and mackerel bait (Scomber scombrus linnaeus, 1758) was evaluated against the industry standard 9/0 J-hooks with squid bait with respect to reducing sea turtle and shark interactions while maintaining swordfish (Xiphias gladius linnaeus, 1758) and tuna (Thunnus spp.) catch rates. In total, 973,734 hooks were deployed during the study. Individually, circle hooks and mackerel bait significantly reduced both loggerhead [Caretta caretta (linnaeus, 1758)] and leatherback [Dermochelys coriacea (vandelli, 1761)] sea turtle bycatch. The combination of 18/0 circle hooks with mackerel bait was even more effective for loggerhead sea turtles and had a significant increase in swordfish catch by weight. The combination 18/0 circle hooks with squid bait resulted in a significant decrease in the swordfish catch and a significant increase in the catch rate of blue shark [Prionace glauca (linnaeus, 1758)] , bluefin tuna [Thunnus thynnus (linnaeus, 1758)], and albacore tuna [Thunnus alalunga (bonnaterre, 1788)]. With all hook types, mackerel bait resulted in a significant decrease in blue shark, bigeye tuna [Thunnus obesus (lowe, 1839)], and albacore tuna, but significantly increased the catch of porbeagle [Lamna nasus (bonnaterre, 1788)] and shortfin mako (Isurus oxyrinchus rafinesque, 1810).

Effects of Hook and Bait on Targeted and Bycatch Fishes in an Equatorial Atlantic Pelagic Longline Fishery

We examined the effects of different hook style and bait type combinations on the catches of targeted, bycatch, and discarded fishes in equatorial atlantic waters. in total, 221 longline sets (>305,000 hooks) were deployed from portuguese pelagic longline vessels (sElEct-pal project) during the february-october fishing season. Three different hook styles and two bait types were tested: the traditional J-hook was compared to two circle hooks (one non-offset and one with 10° offset), and squid bait was compared to mackerel. catch per unit effort (cpuEs) were calculated and compared between the different hook style and bait type combinations, which indicated that the effects of hook style and bait on the cpuEs were species-specific. for example, swordfish cpuEs were higher with J-hooks baited with squid, while for targeted tunas and blue shark only the bait effect was significant, but with opposite effect (i.e., higher catches of tuna with squid bait and higher catches of blue shark with mackerel bait). for the discarded species, at-haulback mortality was also species-specific. proportions of alive vs dead specimens at time of fishing gear retrieval did not vary significantly by hook style or bait type combinations. The total retained catch was analyzed in value per unit effort (VpuE), and indicated losses in fishery revenue when mackerel was used instead of squid, but not when circle hooks were used instead of J-hooks.

Performance of Non-Offset and 10° Offset 18/0 Circle Hooks in the United States Pelagic Longline Fishery

Industry standard fishing hooks used prior to 2004 during Us commercial pelagic longline (Pll) fishing were the 8/0-10/0 J-hooks with a 20°-25° offset�a lateral deviation of the hook point relative to the hook shaft. However, federal regulations enacted in 2004 require the Us Pll industry to employ circle hooks allowing up to 10° offset during fishing operations. Until recently, there have been no studies directly comparing the performance of non-offset and 10° offset circle hooks in commercial Pll applications. Our study alternated non-offset and 10° offset circle hooks along the gear length on individual Pll deployments in the western north atlantic, gulf of mexico, and Windward Passage in the caribbean sea. The study compared the relative performance of both hook types in terms of: (1) catch rates, (2) percent mortality, and (3) the percentage of deep-hooked target and bycatch species. For swordfish, Xiphias gladius (linnaeus, 1758), several experiments indicate: (1) marginally higher catch rates, (2) significantly lower mortality, and (3) significantly less deep hooking on non-offset than 10° offset circle hooks. Most of the performance differences for blue marlin, Makaira nigricans lacepede, 1802, were insignificant; however, one study produced significantly higher mortality on 10° offset than non-offset circle hooks. The present study suggests that, relative to non-offset circle hooks, 10° offset circle hooks may reduce fishing efficiency and can counteract the conservation benefits commonly associated with circle hooks (e.g., lower mortality). However, additional research is required to assess the effects of offset hooks on tunas, billfishes, and elasmobranchs.

Effects of Hook and Bait on Sea Turtle Catches in an Equatorial Atlantic Pelagic Longline Fishery

Here we report a component of the results of the sElEct-pal project, namely marine turtle bycatch composition and rates, hooking location, and status at haulback and at release for several hook-bait combinations in a portuguese commercial longline fishery targeting swordfish in the atlantic equatorial region. In total, 221 longline sets were deployed during the fishing season (february-october) by the portuguese fleet operating in the area. Three different hook types were tested, traditional J-hook (9/0) and two 17/0 circle hooks (non-offset and 10° offset), but only one bait type was used in each set (Scomber spp. or Illex spp.). Four species of sea turtle were caught, most consisting of the olive ridley, Lepidochelys olivacea (Eschscholtz, 1829), and leatherback, Dermochelys coriacea (Vandelli, 1761). The highest mean bycatch per unit effort (bpuE) values for both species combined and for the individual species occurred with the J-hook. The 10° offset circle hook baited with mackerel provided a reduction of 88% and 85% on the bycatch rates, for all turtles combined and olive ridleys, respectively. Although hook location was species-specific and only bait appeared to be driving bycatch rate differences, most sea turtles were caught in the mouth, except for leatherbacks. Only hook type contributed significantly to haulback mortality, with J-hooks associated with slightly higher mortality rates.

Relationship Between Hook Type and Hooking Location in Sea Turtles Incidentally Captured in the United States Atlantic Pelagic Longline Fishery

Because incidental capture in pelagic longline fishing gear potentially kills or injures thousands of sea turtles annually, solutions to reduce the frequency and mortality rate of these interactions are critical conservation priorities. Understanding factors that affect post-hooking mortality rates remains an important component to evaluating the population-level impact of these interactions. Post-release mortality may be dependent upon the nature of the interaction (hooking location and/or entanglement) and amount of gear remaining at release. Hooking location can impact the ability of the crew to remove gear, as deeply ingested hooks cannot be removed safely. We examined the effects of hook type (circle vs J-hooks), offset (degrees), and other factors on hooking location in leatherback, Dermochelys coriacea (Vandelli, 1761), and loggerhead, Caretta caretta (linnaeus, 1758), sea turtles incidentally captured from 2000 to 2010 using fishery observer data. Significant differences in hooking location in loggerheads were observed between offset J-hooks and non-offset and 10° offset circle hooks; loggerheads were most often mouth/beak hooked with circle hooks, whereas most had swallowed offset J-hooks. Greater offsets appear to increase the frequency of deeply ingested hooks. Leatherback sea turtles were predominately externally hooked regardless of hook type, but mouth hookings occurred significantly more often on non-offset (0°) circle and J-hooks than on 10° offset circle hooks. When combined with outreach and education on careful release protocols, the use of circle hooks may increase post-interaction survival by modifying hooking location and facilitating maximum gear removal.

Hook Effects on Seabird Bycatch in the United States Atlantic Pelagic Longline Fishery

Recent studies suggest that use of circle hooks can reduce the incidental mortality of some marine fishes and sea turtles in longline fisheries. Analysis of data from the Us national Marine fisheries service pelagic observer program (pop) revealed a significant hook effect on seabird bycatch. Our analysis focused on the three areas with highest seabird bycatch, the northeast Us coast (60°W-71°W, 35°n-42°n), the Middle atlantic bight (71°W-82°W, 35°n-41°n), and the south atlantic bight (71°W-82°W, 30°n-35°n). We developed two generalized linear models to examine effects of four hook treatments, i.e., four combinations of hook type and size (8/0 J-hook, 9/0 J-hook, 16/0 circle hook, and 18/0 circle hook), on: (1) the probability of catching seabirds on a set and (2) the positive catch rate (i.e., number of seabirds per 1000 hooks in longline sets with at least one seabird caught). Results indicated that combinations of hook type and size significantly influenced the probability of catching seabirds in the United states atlantic pelagic longline fishery. Use of the 8/0 J-hook led to the highest probability of catching a seabird. Use of circle hooks may significantly reduce seabird bycatch in the Us atlantic pelagic longline fishery, but its effectiveness may be confounded by other factors such as bait type, fishing location, season, and target species. Results of our study were limited by the small number of seabird captures in the pop data.

Bycatch susceptibility in pelagic longline fisheries: are albatrosses affected by the diving behaviour of medium-sized petrels?

Species of petrels and shearwaters with high diving ability could facilitate the catch of albatrosses in pelagic longline fisheries, because they retrieve bait to the surface from depths that albatrosses cannot reach. Once on the surface, large seabirds such as albatrosses can easily displace smaller species thus gaining access to baited hooks which increases their likelihood of getting caught. This paper evaluates the extent to which diving species (i.e. Procellaria aequinoctialis, Procellaria conspicillata and Puffinus gravis) increase the susceptibility of albatross to bycatch in pelagic longline fisheries. In 48 sets, attacks on baits were quantified. When more than one bird (of the same or different species) tried to attack the same bait this was defined as a multiple attack. There were 384 attacks on baits, of which 260 were made by a single individual and 124 by more than one. Multiple attacks were the largest source of bycatch of albatrosses (22 of 27 albatrosses whose attacks were observed). Of the baits attacked by albatrosses (n = 244), 17% were indirectly facilitated by diving medium-sized petrels. Considering only the multiple attacks in which albatrosses participated (n = 114), 36% were initiated by these medium-sized petrels. Eleven (41%) of the albatrosses captured, and whose attacks were observed, resulted from a diving medium-sized seabird species first having contacted the terminal tackle. This paper shows that medium-sized petrels, with a strong ability to dive, increase considerably the access to bait, and indirectly, the incidental bycatch of albatrosses. Observations made in the absence of mitigation measures also provide useful information to improve the performance of tori lines. Based on the seabird behaviour, it is recommended that tori lines should have a minimum aerial coverage of 50 m. Copyright © 2012 John Wiley & Sons, Ltd.

Odontocete bycatch and depredation in longline fisheries: A review of available literature and of potential solutions

AbstractOperational interactions between odontocetes (i.e., toothed whales) and longline gear are a global phenomenon that may threaten the conservation of odontocete populations and the economic viability of longline fisheries. This review attempts to define the issue, summarize the trends and geographical extent of its occurrence over the last half century, explore the potential impact on odontocetes and on fisheries, and describe potential acoustic and physical mitigation solutions.Reports of odontocete bycatch rates are highly variable (between 0.002 and 0.231 individuals killed per set) and at least 20 species may be involved. Information about marine mammal population size, migration patterns and life history characteristics are scarce, although at least one population may be in decline due to losses attributable to longline bycatch. Information about the financial impact of depredation on pelagic longline fisheries is also scarce, although estimates of daily fleet‐wide losses range between US$1,034 and US$8,495 (overall fleet income was not reported). Such biological and financial losses may be unsustainable.Recent developments in acoustic and physical mitigation technologies have yielded mixed results. Acoustic mitigation technologies have no moving parts, although require complex electronics. To date, they are insufficiently developed and their efficacy has been difficult to assess. Physical mitigation technologies generally require complex moving parts, although they are relatively simple to develop and assess. Further development and testing remains necessary before widespread implementation would be possible. Development of these approaches should be prioritized and a “toolbox” of various strategies and solutions should be compiled, because a single panacea to the problem is unlikely to emerge.

Ecological Risk Assessment for seabird interactions in Western and Central Pacific longline fisheries

The risk of seabird–fishery interactions in the Western and Central Pacific Ocean (WCPO) was examined by analysing the overlap of seabird distributions with tuna and swordfish pelagic longline fisheries managed by the Western and Central Pacific Fisheries Commission (WCPFC) and its constituent members. The study used spatially-explicit Productivity–Susceptibility Analysis (PSA). Key data inputs were species productivity, fishing effort, likelihood of capture and species density by region. The outputs tailored results to the needs of fisheries- and wildlife-managers, indicating areas of greatest risk of species interactions, species of greatest concern for population impacts, and the flags or fisheries most likely to contribute to the risk. Large albatross species were found to be most likely to suffer population effects when exposed to longline fishing activity, followed by the larger petrels from the genuses Procellaria, Macronectes and Pterodroma. A mixture of coastal states with nesting seabird populations in their Exclusive Economic Zones (New Zealand, Australia and United States of America), distant water fishing nations (Japan, Taiwan) and flags of convenience (Vanuatu) contributed 90% of the risk to seabird populations. Recommendations include enhancing the level of fisheries observer monitoring in areas indicated as high to medium risk for seabird interactions, and consideration of spatial management tools, such as more intensive or more stringent seabird bycatch mitigation requirements in high- to medium-risk areas. The methods used, and similar studies conducted in the Atlantic Ocean could lead to improved targeting of monitoring resources, and greater specificity in the needs for seabird-mitigation measures. This will assist in reducing seabird mortality in longline fishing operations and with more effective use of resources for fishery managers in both domestic fisheries and RFMOs.

Dolphinfish Bycatch in Spanish Mediterranean Large Pelagic Longline Fisheries, 2000–2010

The aim of this paper is to describe the dolphinfish bycatch rates in the longline fisheries of the Western Mediterranean and modelling the nominal bycatch abundance and distribution of dolphinfish from the Spanish Mediterranean as a function of technical, geographical, and seasonality factors. Our results indicate that the impact of the pelagic and semipelagic longline on the dolphinfish population is relatively low (1.083 fishes per 1000 hooks), in contrast with the greater effect on the target species population. We obtained a statistically significant logistic model, with the following factors: technical characteristics of the fishery, geographical location, and seasonality. Drifting surface longliners targeting albacore is the gear with the highest effect on Mediterranean dolphinfish population. The technical characteristics of the fishery and seasonality factors have an important role in explaining the absence or presence of dolphinfish bycatch in the different boat strata, gear types, and seasons. Moreover, sea surface temperature and lunar phases also present additional explanations. Lunar phase as SST has been frequently used as an explanatory variable affecting catch rates of dolphinfish.

Age and growth of the bigeye thresher shark,Alopias superciliosus, from the pelagic longline fisheries in the tropical northeastern Atlantic Ocean, determined by vertebral band counts

The bigeye thresher, Alopias supercilious, is commonly caught as bycatch in pelagic longline fisheries targeting swordfish. Little information is yet available on the biology of this species, however. As part of an ongoing study, observers sent aboard fishing vessels have been collecting set of information that includes samples of vertebrae, with the aim of investigating age and growth of A. supercilious. A total of 117 specimens were sampled between September 2008 and October 2009 in the tropical northeastern Atlantic, with specimens ranging from 101 to 242 cm fork length (FL) (176 to 407 cm total length). The A. supercilious vertebrae were generally difficult to read, mainly because they were poorly calcified, which is typical of Lamniformes sharks. Preliminary trials were carried out to determine the most efficient band enhancement technique for this species, in which crystal violet section staining was found to be the best methodology. Estimated ages in this sample ranged from 2 to 22 years for females and 1 to 17 years for males. A version of the von Bertalanffy growth model (VBGF) re-parameterised to estimate L0, and a modified VBGF using a fixed L0 were fitted to the data. The Akaike information criterion (AIC) was used to compare these models. The VBGF produced the best results, with the following parameters: Linf = 293 cm FL, k = 0.06 y–1 and L0 = 111 cm FL for females Linf = 206 cm FL, k = 0.18 y–1 and L0 = 93 cm FL for males. The estimated growth coefficients confirm that A. supercilious is a slow-growing species, highlighting its vulnerability to fishing pressure. It is therefore urgent to carry out more biological research to inform fishery managers more adequately and address conservation issues.

Age and growth of the smooth hammerhead shark,Sphyrna zygaena, in the Eastern Equatorial Atlantic Ocean, using vertebral sections

The smooth hammerhead shark Sphyrna zygaena (Sphyrnidae) is regularly caught as bycatch in pelagic longline fisheries, but is one of the least studied of all pelagic sharks. Recently, ICCAT (International Commission for the Conservation of Atlantic Tunas) issued recommendations underlining the need for more studies on the life history parameters of this and other pelagic shark species. To this end, the age and growth of S. zygaena were studied in the Eastern Equatorial Atlantic Ocean, in an area where growth parameters were not yet available for this species. Data from 139 specimens, caught between June and September 2009, ranging in size from 136 to 233 cm fork length (FL), were analysed. Preliminary trials were carried out to assess the most efficient growth band enhancement technique. These indicated that sectioning the vertebrae into 500 μ m sections followed by staining with crystal violet produced the best results. Growth models were fitted using the traditional von Bertalanffy growth equation and a modification of this equation using a known size at birth. Growth models were compared using the Akaike information criterion (AIC). The von Bertalanffy growth equation seemed to be the most adequate model to describe growth in this species, with resulting growth parameters of L inf = 272 cm FL, k = 0.06 year for males and L inf = 285 cm FL, k = 0.07 year for females. In the first four years of life, S. zygaena grows 25 cm per year on average, but its growth slows down in later life. Future stock assessment models should incorporate these age and growth parameters for species management and conservation.