Content uploaded by Michelle R Heupel
Author content
All content in this area was uploaded by Michelle R Heupel
Content may be subject to copyright.
A preview of the PDF is not available
Ecological risk assessment of pelagic sharks caught in Atlantic pelagic longline fisheries
Abstract and Figures
An ecological risk assessment (ERA; also known as productivity and susceptibility analysis, PSA) was conducted on eleven species of pelagic elasmobranchs (10 sharks and 1 ray) to assess their vulnerability to pelagic longline fisheries in the Atlantic Ocean. This was a level-3 quantitative assessment consisting of a risk analysis to evaluate the biological productivity of these species and a susceptibility analysis to assess their propensity to capture and mortality in pelagic longline fisheries. The risk analysis estimated productivity (intrinsic rate of increase, r) using a stochastic Leslie matrix approach that incorporated uncertainty in age at maturity, lifespan, age-specific natural mortality and fecundity. Susceptibility to the fishery was calculated as the product of four components, which were also calculated quantitatively: availability of the species to the fleet, encounterability of the gear given the species vertical distribution, gear selectivity and post-capture mortality. Information from observer programs by several ICCAT nations was used to derive fleet-specific susceptibility values. Results indicated that most species of pelagic sharks have low productivities and varying levels of susceptibility to pelagic longline gear. A number of species were grouped near the high-risk area of the productivity-susceptibility plot, particularly the silky (Carcharhinus falciformis), shortfin mako (Isurus oxyrinchus), and bigeye thresher (Alopias superciliosus) sharks. Other species, such as the oceanic whitetip (Carcharhinus longimanus) and longfin mako (Isurus paucus) sharks, are also highly vulnerable. The blue shark (Prionace glauca) has intermediate vulnerability, whereas the smooth hammerhead (Sphyrna zygaena), scalloped hammerhead (Sphyrna lewini), and porbeagle (Lamna nasus) sharks are less vulnerable, and the pelagic stingray (Pteroplatytrygon violacea) and common thresher (Alopias vulpinus) sharks have the lowest vulnerabilities. As a group, pelagic sharks are particularly vulnerable to pelagic longline fisheries mostly as a result of their limited productivity.
Figures - uploaded by Michelle R Heupel
Author content
All figure content in this area was uploaded by Michelle R Heupel
Content may be subject to copyright.
... Como características biológicas generales podemos decir que los grandes tiburones pelágicos presentan maduraciones tardías, tasas de fecundidad relativamente bajas, y un crecimiento lento asociado a una larga longevidad, características que les confieren una acusada susceptibilidad o vulnerabilidad frente a las actividades intensivas de pesca y sobrexplotación (Camhi and Pikitch, 2008;Cortés et al., 2010;Campana, 2016;Dulvy et al., 2021;. ...
... De todas formas, continúan existiendo importantes lagunas de conocimiento en el comportamiento reproductivo del marrajo azul (Mollet et al., 2000;Costa et al., 2002). Al igual que otros tiburones, las peculiaridades del ciclo vital (crecimiento lento, baja fecundidad y maduración tardía) hacen a este escualo particularmente susceptible a las actividades de sobrepesca (Mollet et al., 2000;Baum et al., 2003;Dulvy et al., 2008Dulvy et al., , 2021Cortés et al., 2010;Worm et al., 2013;. El marrajo azul es un tiburón que se reproduce por ovoviviparismo aplacentario con oofagia embrional, con una fecundidad de 4 a 25 neonatos, promedio de 11,6 (Garcia- Cortes et al., 2021), que nacen con unos 70 cm TL tras una gestación de 12 a 18 meses y un ciclo reproductivo de 3 años (Mollet et al., 2000(Mollet et al., , 2002, (Tabla 9). ...
... Al hacer la estimación de las capturas de tiburones ETP de toda la flota, se asumió que la forma de operar y las especies capturadas fueron similares en todos los barcos, y que el uso del espacio se mantuvo razonablemente constante a lo largo del tiempo. Tras la expansión del palangre "estilo americano" a principios de la década de 2000, el arte comúnmente utilizado por la flota española, se ha mantenido constante en la gran mayoría de barcos (García- Cortés et al., 2010;Ramos-Cartelle et al., 2014). La principal especie objetivo de la flota también se ha mantenido constante, con los barcos pesqueros centrándose en dos especies objetivo, el pez espada (Xiphias gladius) y la tintorera (Garcia- . ...
In the present work, key aspects of the biology and ecology of the shortfin mako were studied. Feeding habits, analysed in two ocean basins, indicated that pelagic fish and cephalopods were the main prey items. In the South Pacific Ocean, a marked sexual segregation was found, with females being more common in the SE region; this was also the area with a higher abundance of juveniles and of late-stage pregnant females. In the North Atlantic Ocean, large-scale horizontal movements (including trans-Atlantic migrations) were identified and diel vertical behaviour patterns described. Importantly, individuals that performed wider movements away from the tagging location were less at risk from surface longline fishing. Using tagging and recapture data that spanned a ten-year period, survival, dispersal, and fishing mortality rates for both mako and blue sharks were estimated. The presence of plastics and hooks was also observed for both species, in two studied ocean basins. Finally, bycatch rates for other internationally protected shark species that are commonly caught using surface longlines was estimated based on direct observations, which were several times higher than the official reported data. The results presented here are especially relevant for improving the management measures focused on pelagic sharks.
... Uno de esos métodos es la Evaluación de Riesgo Ecológico por Efectos de la Pesca (eraef, por sus siglas en inglés) propuesto por Hobday y colaboradores (2007) y que ha sido utilizado para evaluar el impacto de las pesquerías en tiburones (Braccini et al. 2006;Walker et al. 2007;Tovar et al. 2010;Cortés et al. 2010;Patrick et al. 2010). Este análisis consta de tres niveles: 1) un nivel cualitativo de Análisis de Escala, Intensidad y Consecuencias (sica, por sus siglas en inglés); 2) un análisis semicuantitativo conocido como Análisis de Productividad y Susceptibilidad (psa, por sus siglas en inglés); y 3) un nivel de análisis cuantitativo (p.e. ...
... evaluadas resultaron con una vulnerabilidad media-alta en ambos litorales Smith y colaboradores (1998) determinaron que S. lewini tiene capacidad de recuperación a la sobrepesca relativamente baja, en adición, Soriano-Velásquez y colaboradores (2006) estimaron una disminución poblacional de 6% por año en el sur del Pacífico Mexicano. Sin embargo, varios autores determinaron que S. lewini es menos vulnerable a la presión de pesca en el Atlántico (Cortés 2002;Cortés et al. 2010;Miller et al. 2014a;2014b). Estas diferencias entre cuencas oceánicas pueden deberse tanto a variaciones en los parámetros de historia de vida de la especie, como a diferentes grados de impacto de las flotas pesqueras. ...
... Carcharhinus longimanus se ha descrito con una productividad biológica moderada en el Pacífico Oeste y Central, y como altamente vulnerable a las pesquerías con palangre en el Atlántico (Cortés 2002;Cortés et al. 2010). Esta especie es capturada en las flotas de altura de ambos litorales, sin embargo, su susceptibilidad de pesca es relativamente baja, lo cual puede deberse al poco traslape de la distribución de este tiburón (Ebert et al. 2013) con las zonas de operación de las flotas pesqueras, especialmente la artesanal. ...
La presente obra es resultado de la participación de expertos provenientes del sector gubernamental, académico y privado, con un total de 36 autores que compilaron información contenida en investigaciones científicas y material bibliográfico (tesis de posgrado, libros y artículos científicos).
Sin duda, el contenido facilitará significativamente la labor de la Autoridad Científica cites de México, pues aporta elementos para analizar y emitir DENP de manera oportuna, además de apoyar a las autoridades Administrativa y de Aplicación de la Ley de México para su efectiva implementación de la cites, cuyo tratado internacional es uno de los más efectivos para la gestión de nuestro patrimonio natural, del cual dependen la subsistencia y modos de vida en el largo plazo de las comunidades pesqueras.
... Uno de esos métodos es la Evaluación de Riesgo Ecológico por Efectos de la Pesca (eraef, por sus siglas en inglés) propuesto por Hobday y colaboradores (2007) y que ha sido utilizado para evaluar el impacto de las pesquerías en tiburones (Braccini et al. 2006;Walker et al. 2007;Tovar et al. 2010;Cortés et al. 2010;Patrick et al. 2010). Este análisis consta de tres niveles: 1) un nivel cualitativo de Análisis de Escala, Intensidad y Consecuencias (sica, por sus siglas en inglés); 2) un análisis semicuantitativo conocido como Análisis de Productividad y Susceptibilidad (psa, por sus siglas en inglés); y 3) un nivel de análisis cuantitativo (p.e. ...
... evaluadas resultaron con una vulnerabilidad media-alta en ambos litorales Smith y colaboradores (1998) determinaron que S. lewini tiene capacidad de recuperación a la sobrepesca relativamente baja, en adición, Soriano-Velásquez y colaboradores (2006) estimaron una disminución poblacional de 6% por año en el sur del Pacífico Mexicano. Sin embargo, varios autores determinaron que S. lewini es menos vulnerable a la presión de pesca en el Atlántico (Cortés 2002;Cortés et al. 2010;Miller et al. 2014a;2014b). Estas diferencias entre cuencas oceánicas pueden deberse tanto a variaciones en los parámetros de historia de vida de la especie, como a diferentes grados de impacto de las flotas pesqueras. ...
... Carcharhinus longimanus se ha descrito con una productividad biológica moderada en el Pacífico Oeste y Central, y como altamente vulnerable a las pesquerías con palangre en el Atlántico (Cortés 2002;Cortés et al. 2010). Esta especie es capturada en las flotas de altura de ambos litorales, sin embargo, su susceptibilidad de pesca es relativamente baja, lo cual puede deberse al poco traslape de la distribución de este tiburón (Ebert et al. 2013) con las zonas de operación de las flotas pesqueras, especialmente la artesanal. ...
El Tiburón sedoso, Carcharhinus falciformis, tiene una distribución circunglobal, se localiza tanto en el Atlántico Occidental y Pacífico Oriental. En México, C. falciformis se encuentra en el Pacífico Mexicano, incluyendo el Golfo de California, así como en el litoral del Golfo de México y Mar Caribe. Los tiburones sedosos habitan generalmente plataformas continentales e insulares, pendientes e incluso se han registrado ocasionalmente en aguas someras (18 m) hasta profundidades de 550 m.
La edad máxima estimada para C. falciformis varía considerablemente para las distintas poblaciones, desde ocho a 11 años hasta más de 30 años. Los parámetros de crecimiento son también altamente variables, con longitudes asintóticas que van de 240 cm a 340 cm de LT (longitud total). El Tiburón sedoso presenta una estrategia de reproducción vivípara placentaria, con un periodo de gestación de 11 a 12 meses y una fecundidad de una a 25 crías con tallas entre 50 y 83 cm (LT). En el 2014 C. falciformis fue enlistada en el Apéndice II de la Convención sobre la Conservación de las Especies Migratorias de Animales Silvestres (CMS) y en 2017 se incluyó en el Apéndice II de la Convención sobre el Comercio Internacional de Especies Amenazadas de Fauna y Flora Silvestres (CITES). En México, la falta de información de captura y esfuerzo pesquero específico ha complicado la evaluación
del estado de las poblaciones de tiburones, en donde C. falciformis no es la excepción. Por ello, es necesario hacer registros específicos de las capturas,
esfuerzo pesquero, datos biológicos-pesqueros, con el fin de realizar análisis demográficos y proyecciones del efecto de la pesca en el stock e identificar
áreas de importancia para su protección.
... PSAs are efficient because they can analyse multiple stocks at the same time and identify species that require additional management attention, due to their highly vulnerable score on the fishing impacts. They are widely used by decision-makers around the world, as they identify species with the highest risk of fishing impact [23][24][25][26][27][28][29]. Recently, Torres et al. [30] performed a PSA focusing on the vulnerability of Azorean coastal fish species. ...
... The PSA approach has been applied globally to various marine animals [25,27,29,43,[45][46][47][48] and is recommended by the Marine Stewardship Council for fishery certifications [49], the Australian Fisheries Management Authority [23], the International Commission for the Conservation of Atlantic Tunas (ICCAT) [27,50], it is used by the Expert Groups of the International Council for the Exploration of the Sea [51], and are used to manage US fish stocks [24]. ...
Small-scale fishing is a multi-gear activity that focuses on a wide range of species. As there is a considerable diversity of species, it is often difficult to keep track of all of those that are caught, and due to the lack of data or poor quality, most stock statuses are currently unknown around the world. Therefore, local ecological knowledge provided by fishers has been regarded as a valuable source of information to bridge these crucial gaps. This study assesses the vulnerability status of 22 fishing stocks in the Azores, through productivity and susceptibility analyses (PSAs) using two independent data sources: conventional scientific knowledge and fishers’ knowledge data. We created four PSAs with separate and integrated data sources. Although we found some differences in the vulnerability scores and rankings, the risk outputs of the PSAs using independent and integrated sources of data generally match, reflecting a similar pattern trend. The findings of this work suggest that integrating FK may be an alternative to provide good fisheries’ assessment outcomes in the absence of CSK. Overall, this research supports the inclusion of fishers’ knowledge in vulnerability assessments as not only beneficial in the absence of data, but also as a supplement to data that can improve management advice.
... On the other hand, the scarcity of empirical baseline catch data for many species has led researchers to develop alternative techniques to establish reliable species risk assessments, such as fuzzy logic analysis (Cheung et al., 2005(Cheung et al., , 2007, Bayesian models (Punt & Hilborn, 1997), extinction risk to global anthropogenic pressures (Dulvy et al., 2014), productivity-susceptibility-based assessments (Astles et al., 2006(Astles et al., , 2009Cortés et al., 2009Cortés et al., , 2015Osio et al., 2015), and the "Robin Hood" approach (Punt et al., 2011). Despite the scientific value of the information provided, they appear very technical and complex to be replicated on a reduced scale. ...
Based on an explorative but rigorous elicitation framework, we obtained the bycatch
fishing probability at the fishing fleet segment level using expert estimates. Based on
the knowledge of three scientific experts, we developed a new and creative structured
method for smart and fast fishery-related
risk assessments for species of high
conservation concern. In order to test the method here propose, we applied it to 76
cartilaginous fish species (included in the IUCN Red Lists) and on five different fishing
segments at both Italian and Mediterranean scale. The method produced qualitative
results specific to the threat posed by fishing for each species and each segment
with information between and within the segments. Based on the interpretation of
resilience–disturbance
interactions developed for ecological systems, the quantitative
results provided reliable cumulative metrics, measuring the extinction risk due to
fishing and the response to overfishing for the species considered. Additionally, the
results highlight that the method perform best on a small geographic scale. Therefore,
the application of this new method on other subregional or local scales where very
few data are available (e.g., fishing effort) could be a valuable tool for the preliminary
assessment for species of conservation concern. In fact, despite the absence of detailed
catch data at local geographic scales, the flexibility of this method could help to
highlight potential fishery-related
conservation problems and thus redirect conservation
strategies for threatened marine species such as many sharks and rays species.
K E YWORDS
elasmobranchs, fishing fleet's segments, IUCN red lists, priority species, risk assessment
... First, future studies could design other types of hotspot indices, and compare the predictions of the alternative types of hotspot indices in several regions. For instance, as bycatch is particularly a concern for the species that have a "slow" life history (a.k.a are K-selected species, i.e., are long-lived, late-maturing, and have a low natural mortality; Cortés et al., 2010;Lewison et al., 2014;Howell et al., 2015), one could develop new composite hotspot index taking the life history of the study species/species groups into account ("life-history weighted hotspot index"). In this setting, the K-selected species that are more likely to be impacted by even low bycatch rates would be given a higher weight. ...
An economically-important Antarctic toothfish (Dissostichus mawsoni) longline fishery operates in the Ross Sea region (RSR), in the Southern Ocean. Management of this fishery according to Article II of the Convention on the Conservation of Antarctic Marine Living Resources aims to minimise the risk of depletion of the species that are caught as bycatch. We employed spatio-temporal models fitted to catch rate data reported by fishing vessels between 2003 and 2020 to understand the spatio-temporal abundance patterns of the major species groups caught as bycatch in the RSR Antarctic toothfish fishery. The study region consisted of the areas of the RSR where fishing has occurred since the inception of the longline fishery. The study species groups included macrourids (Macrouridae), skates (Rajiformes), icefish (Channichthyidae), eel cods (Muraenolepididae) and morid cods
(Moridae). The Akaike information criterion-selected models included the effect of bottom depth and, often, also the effect of surface chlorophyll-a concentration. We found that bottom depth explained only a very small proportion of the variance in the data, while surface chlorophyll-a concentration explained very little of the
variance. The predicted long-term trends of three species groups were clear: the relative abundance of macrourids has decreased, while those of skates and icefish have increased. We resampled from the predictive distributions to identify the abundance hotspots of each of the species groups, defined as the areas where long-term log-relative abundance (i.e., mean log-relative abundance over the study period) was at or greater than the average long-term log-relative abundance over the entire study region. From these abundance hotspots for the individual species groups, we developed two alternative composite hotspot indices. Both composite hotspot indices were highest on the Ross Sea continental shelf slope, between 160◦E and 175◦W. Our results can be used to guide the setting of bycatch limits and inform fishing vessels about bycatch species abundance hotspots in the RSR. We also recommend that future modelling studies seek to disentangle the direct and indirect impacts of the RSR Antarctic toothfish fishery on the bycatch species which are also prey of Antarctic toothfish
... However, the conservation success of these international treaties is highly dependent upon domestic-level implementation, which is lacking for smooth hammerheads in many regions (Rigby et al., 2019). Targeted or bycatch exploitation of smooth hammerheads remains one of the main risks to this species (Corteś et al., 2010;Rigby et al., 2019), with inaccurate catch data and heavy fishing pressure in data-poor regions obscuring the actual effect of this threat (Rigby et al., 2019). ...
The coastal waters of South Africa are habitat to a diverse composition of sharks that are vulnerable to exploitation, many of which are endemic and/or classified by the International Union for Conservation of Nature (IUCN) Red List as Threatened or Data Deficient. Accordingly, this region has been identified as a global research and conservation priority for elasmobranchs. The De Hoop Marine Protected Area (MPA), in the Western Cape Province of South Africa, provides 288 km2 of no-take protection within its boundaries. However, the region experiences heavy commercial fishing, with two vessels actively operating as dedicated shark longliners (as of 2022). When crossing MPA boundaries, sharks are susceptible to capture by these vessels. Utilizing passive acoustic telemetry, the present study evaluated the movements of a threatened juvenile shark species, the smooth hammerhead (Sphyrna zygaena), both inside and adjacent to the De Hoop MPA, and along the greater coastline. Movement data from 20 tagged sharks were used to explore the effects of spatial, environmental, and management variables on their residency and movement patterns. Results indicate a high reliance of sharks on unprotected waters immediately adjacent to the MPA’s eastern boundary, an area of high biological productivity due to its proximity to the mouth of an estuary. Although some tagged sharks did move regionally along the South African coastline, individuals spent 95% of their days detected just outside the eastern boundary of the MPA, rendering them vulnerable to commercial shark longlining occurring there. These findings have conservation implications for smooth hammerhead sharks in South Africa and present an opportunity to revisit management practices that may optimize spatial protection for an important life stage of this threatened species.
... One of the main problems related to mixed-species fisheries is that declines or even collapse of less productive species could be masked by more productive species (Dulvy et al. 2000). Taking into account the lack of species-specific landing data for most of the skates exploited in Argentina, development of biological data-based methods (e.g., demographic analysis, ecological risk assessment) are very important to assess the vulnerability and productivity of skate species (Cortés et al. 2010;CTMFM 2018;Liu et al. 2021). Demographic analysis is a useful tool to focus conservation efforts within a group of exploited species (Cortés 2002;Barnett et al. 2013;Smart et al. 2020) and to provide important information for classical stock assessment models (Mc Allister et al. 2001;Carvalho et al. 2014). ...
More than thirty-three skate species have been registered in the Southwestern Atlantic Ocean south of 34°S (SAO), where hotspots of the endemic threatened marine chondrichthyans with high scientific and conservation priorities have been detected. The lack of specie-specific landing data, highlights the importance of biological data-based methods to determine the vulnerability and productivity of skate species. In this work we estimated the demographic parameters for the skates Atlantoraja castelnaui, Rioraja agassizi, Sympterygia bonapartii and Zearaja brevicaudata in SAO, by implementing Leslie matrix models. The finite rate of population growth (ʎ) for the four skate’s species ranged from 1.036 (Z. brevicaudata) to 1.196 (R. agassizi). Elasticity analyses and the performance of different harvest strategies show that reducing juvenile catches appears to be one of the most effective management actions for these species since they result in higher survivorship of age classes with more influence in λ. Differences in the biological productivity of the skates suggests that, in order to achieve sustainable exploitation of skates, the commitment of all stakeholders to improve species-level information is necessary.
... In the Ecological Risk Assessment (ERA) ranking for longline gear, mako sharks have been allocated the highest vulnerability level (No. 1) [93]. In the models without F, the mean population growth rates in this study (λ = 1.098 and 1.063 year −1 for the 2-and 3-year reproductive cycle models, respectively) were moderately higher than those derived from previous demographic analyses [20,94,95]; moreover, they differed considerably from those reported by Cortés [52] (Table 5). The reasons underlying these differences are diverse, with the most typical being the use of different models (single-sex vs. two-sex, age-structured vs. stage-structured, Bayesian surplus production model) and life history parameters (e.g., Ms and population growth rate) in the aforementioned studies; moreover, the findings for mako sharks in the South Pacific Ocean may not be applicable to those in other oceans, since the shark populations in the different oceans have varying traits. ...
The shortfin mako shark (Isurus oxyrinchus) demonstrates low productivity and is thus relatively sensitive to fishing. Natural mortality (M) and fishing mortality (F) data are critical to determine their population dynamics. However, catch and fishing effort data are unavailable for this species in the South Pacific Ocean, making stock assessments difficult. Demographic quantitative methods aid in analyzing species with limited data availability. We used a two-sex stage-structured matrix population model to examine the demographic stock status of mako sharks. However, data-limited models to determine fishery management strategies have limitations. We performed Monte Carlo simulations to evaluate the effects of uncertainty on the estimated mako shark population growth rate. Under unfished conditions, the simulations demonstrated that the mako sharks showed a higher finite population growth rate in the 2-year reproductive cycle compared to the 3-year reproductive cycle. Protecting immature mako sharks led to a higher population growth rate than protecting mature mako sharks. According to the sex-specific data, protecting immature male and female sharks led to a higher population growth rate than protecting mature male and female sharks. In conclusion, sex-specific management measures can facilitate the sustainable mako shark conservation and management.
The shortfin shark Isurus oxyrinchus plays essential ecological and economic roles in all oceans as it is a top predator and, while being a bycatch of the longline fishery, it is a critical fishing resource for many fishing fleets. Their reproductive parameters are still poorly known in some ocean basins, such as the South Atlantic, mainly due to the lack of sampling of mature females. In this work, we study the reproductive biology of I. oxyrinchus in the southwestern South Atlantic Ocean (SWAO) describing primary and secondary sexual characteristics and determining size at first maturity using a Bayesian approach. Individuals were collected in commercial pelagic longline fisheries in SWAO between November 2020 and July 2021. Males ranged from 115 to 295 cm total length (TL) and females from 141 to 239 cm TL. Histological analyzes showed the development of radial-type seminiferous follicles for males, an ovary with a labyrinthine lumen for females and at least five different maturation stages for both sexes. The size at maturity for females was estimated at 282 cm TL and 194 cm TL for males. These reproductive parameters were different from some estimated for other oceanic regions. With the updated reproductive parameters, we analyzed the use of the study area by different stages of life between 2018 and 2022. We found that individuals from different stages of life use the study area differently throughout the year and over the years. The updated reproductive parameters for the South Atlantic will inform future assessments of stocks and management, especially for females, for which TL50 should be considered as an initial approximation. Evidence of heterogeneous use of the study area can be seen as evidence of the lack of stock structuring in the region, so management measures are recommended at a regional rather than a local level.
The bycatch of Australia's northern prawn fishery (NPF) comprises 56 elasmobranch species (16 families). The impact of this fishery on the sustainability of these species has not been addressed. We obtained estimates of catch rates and the within-net survival of elasmobranchs. Carcharhinus tilstoni, C. dussumieri, Rhynchobatus djiddensis, and Himantura toshi represented 65% of the bycatch. For most species, >50% of individuals in the bycatch were immature, and some species recruited to the fishery at birth. For all species combined, 66% of individuals in the bycatch died in the trawl net. The relative sustainability of elasmobranchs caught as bycatch was examined by ranking species with respect to their susceptibility to capture and mortality due to prawn trawling and with respect to their capacity to recover once the population was depleted. The species that were least likely to be sustainable were four species of pristids, Dasyatis brevicaudata, and Himantura jenkinsii. These are bottom-associated batoids that feed on benthic organisms and are highly susceptible to capture in prawn trawls. The recovery capacity of these species was also low according to our criteria. Our results provide a valuable first step towards ensuring the sustainability of elasmobranchs that are caught as bycatch by highlighting species for management and research. The effectiveness of turtle excluder devices (TEDs) in reducing elasmobranch bycatch varied greatly among species but was generally not very effective because most of the captured species were small.
Ecosystem-based fisheries management (EBFM) has emerged during the past 5 y as an alternative approach to single-species fishery management. To date, policy development has generally outstripped application and implementation. The EBFM approach has been broadly adopted at a policy level within Australia through a variety of instruments including fisheries legislation, environmental legislation,
and a national policy on integrated oceans management. The speed of policy adoption has necessitated equally rapid development of scientific and management tools to support practical implementation. We discuss some of the scientific tools that have been developed to meet this need. These tools include extension of the management strategy evaluation (MSE) approach to evaluate broader ecosystem-based fishery management strategies (using the Atlantis modelling framework), development of new approaches to ecological risk assessment (ERA) for evaluating the ecological impacts of fishing, and development of a harvest strategy framework (HSF) and policy that forms the basis for a broader EBFM strategy. The practical application of these tools (MSE, ERA, and HSF) is illustrated for the southern and eastern fisheries of Australia.
I quantify the effects of 11 variables on the catchability and fishing power of pelagic longlines, which are used to catch
tunas and billfishes in the open ocean. Extension of the depth range and the duration of longline operations have reduced
the catchability of several epipelagic species, such as mako sharks (Isurus spp.), since industrial longlining commenced in the tropical Pacific Ocean in the early 1950s. Reductions in the body size
of many species may also have reduced encounters with longline hooks. By contrast, the catchability of commercially valuable
bigeye tuna (Thunnus obesus) increased substantially because of the longer duration and extension of the depth range of longlines. Stronger and less
visible line materials and increased fishing-master experience also contributed to increased catchability. By affecting the
rate of bait loss, the introduction of new bait species increased fishing power. This study highlights significant problems
in deriving indices of abundance from commercial catch and effort data. Instead of relying on commercial data, assessments
should use tag-recapture experiments or dedicated surveys to obtain fishery-independent estimates of abundance.
There is mounting evidence of recent declines in a number of elasmobranch populations as a result of overharvesting (Campana et al., 1999, 2001, 2002; Simpfendorfer, 2000; Cortés et al., 2002; Baum et al., 2003), and two species of skate have even become locally extirpated or almost extinct (Brander, 1981; Casey and Myers, 1998). Yet our knowledge of life history traits of most species is still limited and we are just beginning to gain insight into the life history patterns shared by some species and the relationships among life history traits (Compagno, 1990; Cortés, 2000; Frisk et al., 2001). Within the past two decades, our scant but increasing knowledge of the life history of numerous species (Compagno, 1984) has given rise to the development of demographic (life table and matrix population) models for elasmobranchs that attempt to characterize the vulnerability to exploitation of the populations under study. Increased fishing pressure on some species (Hoff and Musick, 1990), largely due to an increase in demand for shark fins (Bonfil, 1994), also prompted the emergence of population models to assess stock status.
I explored the effect of uncertainty in demographic traits on demographic analyses of sharks, an approach not used before for this taxon. I used age-structured life tables and Leslie matrices based on a prebreeding survey and a yearly time step applied only to females to model the demography of 41 populations from 38 species of sharks representing four orders and nine families. I used Monte Carlo simulation to reflect uncertainty in the estimates of demographic traits and to calculate population statistics and elasticities for these populations; I used correlation analysis to identify the demographic traits that explained most of the variation in population growth rates ( λ ). The populations I examined fell along a continuum of life-history characteristics that can be linked to elasticity patterns. Sharks characterized by early age at maturity, short lifespan, and large litter size had high λ values and short generation times, whereas sharks that mature late and have long lifespans and small litters have low λ values and long generation times. Sharks at the “fast” end of the spectrum tended to have comparable adult and juvenile survival elasticities, whereas sharks at the “slow” end of the continuum had high juvenile survival elasticity and low age–zero survival ( or fertility ) elasticity. Ratios of adult survival to fertility elasticities and juvenile survival to fertility elasticities suggest that many of the populations studied do not possess the biological attributes necessary to restore λ to its original level after moderate levels of exploitation. Elasticity analysis suggests that changes in juvenile survival would have the greatest effect on λ, and correlation analysis indicates that variation in juvenile survival, age at maturity, and reproduction account for most of the variation in λ. In general, combined results from elasticity and correlation analyses suggest that research, conservation, and management efforts should focus on these demographic traits.
The susceptibility to fishing of the populations of 13 sea snake species caught as bycatch by trawlers in Australia’s Northern Prawn (shrimp) Fishery (NPF) was examined to identify species at potential risk that should become priority for research and management. Each species was assessed according to two groups of criteria — (1) their relative vulnerability to capture by prawn trawling and (2) the relative capacity of their populations to sustain increased mortality due to fishing. Within each group, each species was ranked (1–3) on individual criteria reflecting distribution, catch rates, habitat selection, activity patterns, reproductive biology and survival. These criteria were then weighted according to their relative importance. The mean weighted ranks of each species for the two groups of criteria were plotted and zones of relative priority were identified. Only one species, Hydrophis pacificus, fell into the high-priority category, being both highly vulnerable to trawling and having a poor capacity to sustain fishing mortality. However, this species has been very rare in prawn trawl catches for at least 10 years, making it difficult to assess any temporal or spatial changes in catch. Among the species of moderate priority, two large, bulky species — Aipysurus laevis and Astrotia stokesii — had the poorest capacity to sustain fishing mortality of any of the species examined and would become a research and management priority if the percentage of the population vulnerable to capture increased. New fisheries management changes to (1) reduce effective fishing effort and (2) reduce bycatch by inclusion of Turtle Excluder Devices that take effect in 2000 are both expected to reduce the susceptibility of sea snakes to trawling in the NPF. Further studies to better estimate the sizes of sea snake populations and model natural and fishery processes will help clarify if populations of the most susceptible species are indeed at risk.