World Fisheries Congress in Scotland

6th World Fisheries Congress
Sustainable Fisheries in a Changing World

7th – 11th May 2012
Edinburgh, Scotland


Shark-Related Abstracts

Using videography to understand the effects of large marine reserves on pelagic,
migratory species

Gollock, Matthew; Koldewey, Heather; Letessier, Tom; Meeuwig, Jessica
ZSL, United Kingdom; University University of Western Australia, Australia

Large, open-ocean marine protected areas (MPAs) are being advocated and implemented as an essential part of the conservation and management of marine resources. However, it has been argued that MPAs will not be effective in protecting “highly migratory species”. For example, within the recently created Chagos no-take MPA, there is continued pressure for the fishery to reopen, particularly if benefits for tuna and the shark species are not clearly demonstrated. Large, pelagic predators, such as sharks and tuna, are fundamental to marine ecosystem health, but have been seriously affected by industrial fisheries, and populations of a number of species have declined significantly. Historically, only fisheries dependent data has been available and thus has been limited to target species, with little or no information relating to by-catch species. Therefore the establishment and implementation of consistent scientific baselines for pelagic species using safe, non-destructive, low-cost and transferable technology will aid the assessment of the benefits and limitations of large-scale MPAs. A number of monitoring programmes for large, pelagic species have made use of improvements in remote telemetry techniques, particularly satellite tags. Tagging studies provide valuable information on movement patterns and residency of individuals but less information is available on species abundance and size. Stereo baited remote underwater video systems (BRUVS) are an established survey technique for monitoring fish diversity, abundance and size structure and have been used successfully to evaluate the effectiveness of coastal MPAs. This study is adapting BRUVs for use in the pelagic realm, an ecosystem that has been poorly studied within the context of MPAs. The adaptation of this technique to the pelagic environment aims to document the diversity, abundance and size structure of mobile pelagic predators. Sea trials are scheduled in the Perth Canyon, Western Australia, a known aggregation site for pelagic species such as yellowfin tuna (a target species) and blue sharks (a bycatch species). Documenting pelagic species using videography represents a significant technological challenge with innovations required to develop systems that control depth and buoyancy, and determining appropriate attractants such as sound and light in addition to conventional bait. Results from this pilot study and a critique of their benefits for large-scale MPAs such as Chagos, will be presented.


Using observer data, weather buoys and fishers’ knowledge to differentiate fishing decisions from fish behaviour

Carruthers, Erin; Schneider, David
Memorial University, St. John’s, Canada

Catch rates reflect fish behaviour, fishing decisions, and interactions between these two processes. For pelagic longline and other fisheries that use baited gear, catch rates depend upon feeding behaviour. Therefore, differences in the distributions and feeding behaviours of target and bycatch species may be used to identify opportunities to decrease bycatch without decreasing target species catch. We used fisheries observer and concurrent environmental data to determine how fishing decisions and environmental variables affect catch rates of the most common bycatch and landed species in the Canadian pelagic longline fishery (blue shark Prionace glauca; swordfish, Xiphias gladius). Qualitative interview data were used to identify fishing decisions and to describe pelagic species distributions and feeding behaviour. Sets with high blue shark catch rates accounted for most of the bycatch – 10% of the observed sets accounted for close to half of the observed blue shark bycatch. Fishing decisions, such as fishing season, region, or bait type, had little effect on blue shark catch rates but did affect target species catch rates. Expected associations between blue shark catch rates and wind stress, and between swordfish catch rates and lunar cycles were not significant in the generalized linear model analyses. Instead, water temperature was identified as the key environmental variable affecting blue shark catch rates. Further, interviewed longline captains’ observations identified possible ecological mechanisms for this relationship and, therefore, ways to better focus future blue shark bycatch mitigation research.


Heavy fishing puts Brazilian sharks and rays in great trouble

Brick Peres, Monica; Barreto, Rodrigo; Lessa, Rosangela; Vooren, Carolus; Charvet, Patricia; Rosa, Ricardo
Ministério do Meio Ambiente (MMA), Brazil; Universidade Federal Rural de Pernambuco (UFRPE), Brazil;
Fundação Universidade do Rio Grande (FURG), Brazil; Serviço Nacional de Aprendizagem Industrial (SENAI), Brazil;
Universidade Federal da Paraíba (UFPB), Brazil 

Chondrichthyes occurring in Brazilian marine waters were regionally assessed according to the IUCN Red List criteria. For 151 species, around 39% were threatened (18% Critically Endangered-CR, 5%; Endangered-EN; 16% Vulnerable-VU; 1% Regionally Extinct- RE; 9% Near Threatened-NT; 18% Least Concern-LC and 34% Data Deficient-DD); the latter are probably threatened without enough data to quantify their risk of extinction. Species assessed belonged to the families: Alopiidae, Arhynchobatidae, Callorhinchidae, Carcharhinidae, Centrophoridae, Cetorhinidae, Chimaeridae, Dalatiidae, Dasyatidae, Echinorhinidae, Etmopteridae, Ginglymostomatidae, Gymnuridae, Hexanchidae, Lamnidae, Megachasmidae, Mitsukurinidae, Mobulidae, Myliobatidae, Narcinidae, Odontaspididae, Potamotrygonidae, Pristidae, Pseudocarchariidae, Pseudotriakidae, Rajidae, Rhincodontidae, Rhinobatidae, Rhinochimaeridae, Rhinopteridae, Scyliorhinidae, Somniosidae, Sphyrnidae, Squalidae, Squatinidae, Torpedinidae, Triakidae, Triakidae, Urotrygonidae. Nine species of families Alopiidae, Cetorhinidae, Ginglymostomatidae, Mobulidae, Pristidae, Rhincodontidae, Sphyrnidae, Torpedinidae were assessed as threatened. The Carcharhinidae family, which is has the highest number of species is heavily exploited totaling 56 % of species in risk of extinction categories. The excessive fishery is the main threat for about 90% marine species. Results are compatible with the strategy of high longevity (9 to 70 years-old), low fecundity and late maturity. Although 34% of assessed marine species had unknown fecundity, around 50% have mean annual litter below 10 puppies. A great number of species performs aggregations, which makes them easy targets to fisheries leading to low population levels. Many species are threatened due to incidental catches, particularly when they aggregate for giving birth and mating. All fisheries for elasmobranchs did collapsed after few years due to the open access character of Brazilian fisheries, which are mostly unmanaged. This study shows that heavy and unregulated fisheries are the main threat for marine elasmobranchs driving them to great risk. The recovery of threatened populations will only occur if directed and non-selective fisheries will be banned or sharply reduced and critical areas protected as no-take marine reserves in short term. Taxonomic uncertainty and scarce past information are still a conservation setback for the Chondrichthyes in Brazil.


Assessing age and maturity in deep-water sharks of the Rockall Trough,
North- East Atlantic: An area of growing deep-water fishery activity

Moore, Daniel; McCarthy, Ian; Neat, Francis
Bangor University, United Kingdom; Marine Scotland, United Kingdom

The Rockall Trough is a rapidly growing region of deep sea fishing activity where elasmobranch bycatch is considerable and this has resulted in the population decline of many deep water shark species. An understanding of the population biology of these species is vital if effective management is to be considered. This study presents new information on the growth and maturation schedules of Galeus melastomus, Centroscymnus crepidater and Apristurus aphyodes sampled from the Rockall Trough. Owing to their deep water habitat these species have been the subject of few studies to date and subsequently their ecology and biology is relatively poorly understood. In addition to the assessment of size and maturity, this study applied an ageing technique using Cobalt (II) Nitrate to stain growth bands in vertebra centra. Growth band pairs were successfully viewed in G. melastomus and pair counts ranged from 0 to 5 in males and 2 to 7 in females respectively. A higher asymptotic length was deduced from the Von Bertalanffy growth equation for females than males (Females: L∞ = 69.3cm, k = 0.370; Males: L∞ = 60.8, k = 0.573). C. crepidater and A. aphyodes growth band enhancement was unsuccessful, likely due to poor calcification of the vertebra centra. In addition to further new data specific to this fishing intensive region, also presented is the first TL50 analysis for Apristurus aphyodes globally.


Cryptic mortality throughout the world’s pelagic longline fisheries

Ward, Peter
Australian Bureau of Agricultural & Resource Economics & Sciences, Australia

The widespread switch from wire traces to nylon leaders is seen as a tremendous benefit in reducing shark bycatch in many pelagic longline fisheries. However, large numbers of animals now escape longlines by biting through nylon leaders. Experiments with the two gear types, for example, reveal that the number of animals lost on nylon leaders is equivalent to the number retained. Sharks that are jaw-hooked and bite through the leader often survive, whereas the fate of those that ingest hooks is largely unknown. In addition to sharks biting through nylon leaders, many small animals, including seabirds and marine turtles, may be removed from hooks by scavengers. These small animals are likely to perish. Research involving underwater cameras and simple additions to data collected by at-sea observers will allow the magnitude of the problem to be evaluated and mitigation measures to be developed.


Population Biology of the Sharpnose shark (Rhizoprionodon longurio) in the Artisanal fishery of the Gulf of California, Mexico

Muhlia-Melo, Arturo; Corro-Espinoza, David1; Marquez-Farías, Fernando
CIBNOR S.C., Mexico; Universidad Autónoma de Sinaloa, Mexico

Sharpnose shark is frequently observed on the artisanal coastal fisheries in the Gulf of California. During the last decade Sonora and Sinaloa have been placed in the top six places of national production of sharks. Basic biology studies have been scarce and are needed to manage these resources as they begin to show decline in their historical catches. 956 individuals were sampled, 456 males and 500 females and 513 free-living embryos, a total of 1.469 specimens. The interval length was 33.5 cm to 134.5 LT, with 80% of individuals between 74.3 and 134.5 cm TL. Males had the range from 39.8 to 119.0 cm TL, with a mean of 88.3 cm TL and mode of 96.0 cm TL. The length-frequency showed three modal groups, corresponding to the juveniles, sub-adults and adults. Growth curves by sex of (Rhizoprionodo longurio) were obtained by mean of the analysis of growth rings in vertebrae. The annual periodicity in the deposition of the age bands was verified by analyzing the marginal increase. Males of (Rhizoprionodon longurio) recorded a maximum length of 119.0 cm LT and a maximum age of 6 years and females a maximum length of 124 cm LT and a maximum age of 7 years. Individuals of both sexes grow at a similar rate until they reach an age of 2 years, then the growth rate decreases in males. Parameters of von Bertalanffy model were estimated based on the age bands in vertebral centra. The parameters derived from age data length are L‡ = 110.54 cm, k = 0.58 year-1 and t0 = -1.49 years for males and L‡ = 124.46 cm, k =0.46 years-1 and t0 = -1.43 years for females. Rhizoprionodon longurio has a short life cycle and is growing faster than most other carcharhinids sharks in the Gulf of California. Information on gonadal maturation showed that females have an average of 7.5 offspring. Males showed that mature sexually and are reproductively active during the spring (April-May) when they have around 100 cm Total length. Socio-economic importance of the fishery This fishery is has a great social and economic impact since it represents the household income of about 10,000 families. R. longurio has an anual reproductive cicle and the presence of juveniles in catches require urgent management measures.


Demographic analysis of oceanic whitetip and crocodile shark in
Southwestern Atlantic Ocean

Santana, Francisco; Duarte-Neto, Paulo; Lessa, Rosangela
Universidade Federal Rural de Pernambuco (UFRPE), Brazil

The oceanic whitetip shark (Carcharhinus longimanus) is an oceanic epipelagic species, with great commercial importance in the southwestern Atlantic, ranking second in abundance of sharks and third in shark fins landed by commercial oceanic longliners in the northeastern of Brazil. The crocodile shark (Pseudocarcharias kamoharai) is a small oceanic shark, without any commercial importance being totally discarded. The objective of the current study is to infer on the status of the C. longimanus and P. kamoharai populations in the southwestern Atlantic Ocean, based on demographic analysis using life-history tables (LHT), Leslie matrices (LM) and stage-based model (SBM). Samples of the two species were collected throughout the South Atlantic Ocean, allowing the input parameters (age at first maturity, longevity, fecundity and natural mortality) to be estimated for the construction of LHT. Those parameters were randomly taken from their respective probability distributions, considering the uncertainty in estimates derived from Monte Carlo Simulations. Each scenario was executed 1000 times with varying input vital rates for the estimation of demographic parameters (net reproductive rate, R0; mean generation length, G; and intrinsic rate of population increase, r). Elasticities were estimated for Leslie and stage-based matrices. For C. longimanus, when fishing mortality was used since the age of recruitment on, the population decreases about -4.9%/year in LHT and LM, and -8.2%/year for SBM. If there were no fisheries, or if thecatches started from the adult stage (7 years), the population would increase more than 2% per year, indicating that the population is overexploited. For P. kamoharai, the scenarios revealed that the exploitation leads to a significant reduction in population for the three models (LHT = -5.8%/year and SBM = -11.3%/year); the context did not improve when just natural mortality was used, because the population continued to decrease (LHT = -1.9%/year and SBM = -5.9%/year). The SB matrix is not an appropriate model for both species, because of the short longevity. Furthermore, the elasticities revealed that the two species have low fecundity and low number of juvenile survivors which are not enough to compensate the mortality by fisheries. Those biological features render both species highly vulnerable for exploitation and the two species can be near the overexploitation.


Demographic analysis of the nari nari freshwater stingray, Paratrygon aiereba,
at Rio Negro Basin, Amazonas State Brazil

Araújo, Maria Lúcia; Lessa, Rosângela; Da Silva, Francisco; Monjelol, Luiz Alberto
UFAM, Brazil; UFRPE, Brazil

The freshwater stingray,Paratrygon aiereba, is found in all aquatics habitat at Amazon Basin. As most of elasmobranch fishes, produces a low number of offspring (two embryos per litter). Informations of population status and natural and anthropogenic impacts on P. aiereba are rare. To obtain the basic data on the biology and demography of P. aiereba, demographic model based on estimates of mortality, longevity and maturity was constructed to assess the conservation status of the nari nari freshwater stingray in the Rio Negro Basin. Monte Carlo simulation was conducted to incorporated uncertainty in life history parameters into model projections. Ten models were tested using deterministic and probabilistic approaches under unexploited and exploited scenarios. Biological information was obtained on stingrays collected at middle Rio Negro Basin
(00030’S, 630012’W). Results indicated that maturity occurred at 58.13cm disc width (5.6 years) in females and 54.63mm (5.4.years) in males, with maximum age estimates of 12.23 and 9.23 years from females and males, respectively. In deterministic approach, population would increased at scenarios were natural mortality was ≤0.245, with mean annual population growth rates (λ) of 1.02–1.152 year-1(2–15.2% increase), net reproductive rates (R0) of 1.158–2.898 and generation times (G) of 7.201 years. When current fishing mortality and anthropogenic impact mortality was taken into account, a decrease in population was observed with λ 0.795 -0.986 y-1 (-20.5% – -1.4%) with a projected reduction of 4.1% over 7.4 years to 20.48 % over 8.32 years. In probabilistic approach, increase in population was observed just in scenario where mx was double of real value, λ of 0.752–1.253 y-1 (24.8 % decreased – 12.53% increased), R0 of 0.061-4.832 and G of 6.53.–10.05 years were projected from probabilistic scenarios. Elasticity analysis indicated that population growth rates for nari nari stingray are more strongly influenced by the survival of juvenile (age 2 to 4) or changes in fecundity than by survival of neonates (age 0 and 1). These results suggest that P. aiereba has a low intrinsic growth potential and limited resilience to fishing pressure. Population collapses can occur through unmonitored fishing effort. Size limit management measures are urgently needed to ensure the sustainable utilisation of the stock.

Source with all Supplementary Information (PDF): 6th WFC – Book of Abstracts




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