Browsing by Author "Erzini, Karim"
Now showing 1 - 10 of 220
Results Per Page
Sort Options
- A comparative study of the species composition of discards from five fisheries from the Algarve (southern Portugal)Publication . Erzini, Karim; Lima Costa, Maria Emília; Bentes, L.; Borges, T. C.Discards from five of the most important fisheries (crustacean trawling, fish trawling, demersal purse seining, pelagic purse seining and trammel netting) in southern Portugal were studied and compared. A total of 236 species of all taxa were discarded, with fish and cephalopods accounting for more than 90% of the discarded biomass, except trammel nets (81%). Although there was some overlapping of species, multivariate analysis using cluster analysis for classification and multidimensional scaling (MDS) for ordination, showed that there were significant differences between the five gears in terms of species composition and biomasses discarded, with the least similarity between crustacean trawling and all other fishing operations. The differences between fisheries were probably as a result of a combination of gear selectivity and depth fished. The results suggest that discarding practices are likely to have different, yet significant impacts on the marine ecosystem, warranting further studies on the fate of discards, the factors influencing discarding and mitigation.
- A conservation trade-off? Interspecific differences in seahorse responses to experimental changes in fishing effortPublication . Curtis, Janelle M. R.; Ribeiro, Joaquim; Erzini, Karim; Vincent, Amanda C. J.1. A 2-year experimental seining programme and underwater visual censuses were undertaken to quantify the direct effects of active demersal fishing on the population structure and relative abundance of two sympatric seahorse species of conservation concern: the European long-snouted seahorse, Hippocampus guttulatus Cuvier 1829 and the short-snouted seahorse, Hippocampus hippocampus L. The influence of habitat preference on population-level responses to changes in habitat structure following a reduction in fishing effort was also investigated. 2. It was predicted that the benthic habitat would be more structurally complex after fishing ceased and that seahorse densities would increase in response to reduced fishing mortality. Furthermore, it was predicted that the magnitude of the increase in density would be greater for H. guttulatus than for H. hippocampus, because the former species prefers complex vegetated habitats while the latter species uses sparsely vegetated habitats. 3. As predicted, the amount of habitat cover increased significantly when seining ceased, primarily through increases in the abundance of drifting macroalgae and unattached invertebrates. Despite similarities in life histories, the two seahorse species responded differently in terms of magnitude and direction to reduced fishing effort: the abundance of H. guttulatus increased significantly while H. hippocampus decreased in abundance. 4. Results suggest that active demersal fishing may influence the magnitude and direction of the responses of benthic marine fishes to exploitation through its impacts on habitat structure. An increase in habitat cover appeared to favour higher densities of H. guttulatus when seining effort was reduced. By contrast, repeated seining, which maintained less complex habitats, appeared to favour greater abundances of H. hippocampus. 5. Given differences in habitat preference among benthic marine fishes subject to incidental capture in fisheries, simultaneous attempts to manage populations of sympatric species may require complementary strategies that support the persistence of diverse habitat types. Copyright (c) 2006 John Wiley & Sons, Ltd.
- A multi-model approach to evaluate the role of environmental variability and fishing pressure in sardine fisheriesPublication . Miguel de Sousa Leitão, Francisco; Alms, V.; Erzini, KarimUnderstanding the fluctuations in population abundance is a central question in fisheries. Sardine fisheries is of great importance to Portugal and is data-rich and of primary concern to fisheries managers. In Portugal, sub-stocks of Sardina pilchardus (sardine) are found in different regions: the Northwest (IXaCN), Southwest (IXaCS) and the South coast (IXaS-Algarve). Each of these sardine sub-stocks is affected differently by a unique set of climate and ocean conditions, mainly during larval development and recruitment, which will consequently affect sardine fisheries in the short term. Taking this hypothesis into consideration we examined the effects of hydrographic (river discharge), sea surface temperature, wind driven phenomena, upwelling, climatic (North Atlantic Oscillation) and fisheries variables (fishing effort) on S. pilchardus catch rates (landings per unit effort, LPUE, as a proxy for sardine biomass). A 20-year time series (1989-2009) was used, for the different subdivisions of the Portuguese coast (sardine sub-stocks). For the purpose of this analysis a multi-model approach was used, applying different time series models for data fitting (Dynamic Factor Analysis, Generalised Least Squares), forecasting (Autoregressive Integrated Moving Average), as well as Surplus Production stock assessment models. The different models were evaluated, compared and the most important variables explaining changes in LPUE were identified. The type of relationship between catch rates of sardine and environmental variables varied across regional scales due to region-specific recruitment responses. Seasonality plays an important role in sardine variability within the three study regions. In IXaCN autumn (season with minimum spawning activity, larvae and egg concentrations) SST, northerly wind and wind magnitude were negatively related with LPUE. In IXaCS none of the explanatory variables tested was clearly related with LPUE. In IXaS-Algarve (South Portugal) both spring (period when large abundances of larvae are found) northerly wind and wind magnitude were negatively related with LPUE, revealing that environmental effects match with the regional peak in spawning time. Overall, results suggest that management of small, short-lived pelagic species, such as sardine quotas/sustainable yields, should be adapted to a regional scale because of regional environmental variability.
- A regulation-based classification system for marine protected areas (MPAs)Publication . Horta e Costa, Bárbara; Claudet, Joachim; Franco, Gustavo; Erzini, Karim; Cara, Anthony; Gonçalves, Emanuel J.Marine protected areas (MPAs) are a global conservation and management tool to enhance the resilience of linked social-ecological systems with the aim of conserving biodiversity and providing ecosystem services for sustainable use. However, MPAs implemented worldwide include a large variety of zoning and management schemes from single to multiple-zoning and from no-take to multiple-use areas. The current IUCN categorisation of MPAs is based on management objectives which many times have a significant mismatch to regulations causing a strong uncertainty when evaluating global MPAs effectiveness. A novel global classification system for MPAs based on regulations of uses as an alternative or complementing, the current IUCN system of categories is presented. Scores for uses weighted by their potential impact on biodiversity were built. Each zone within a MPA was scored and an MPA index integrates the zone scores. This system classifies MPAs as well as each MPA zone individually, is globally applicable and unambiguously discriminates the impacts of uses. (C) 2016 The Authors. Published by Elsevier Ltd.
- A regulation-based classification system for marine protected areas: A response to Dudley et al. [9]Publication . Horta e Costa, Bárbara; Claudet, Joachim; Franco, Gustavo; Erzini, Karim; Caro, Anthony; Gonçalves, Emanuel J.Dudley et al. [9] commented on our paper [11], arguing that the current IUCN objective-based categorization of protected areas, which is also used in marine protected areas (MPAs), should not be abandoned and replaced by the new regulation-based classification system [11]. Here we clarify that we do not advocate replacing the current IUCN categories, but highlight the benefits of using both the objective-based IUCN categories and the new regulation-based classification when applied to MPAs. With an increasing number of MPA types being implemented, most of them multiple-use areas zoned for various purposes, assessing ecological and socio-economic benefits is key for advancing conservation targets and policy objectives. Although the IUCN categories can be used both in terrestrial and marine systems, they were not designed to follow a gradient of impacts and there is often a mismatch between stated objectives and implemented regulations. The new regulation-based classification system addresses these problems by linking impacts of activities in marine systems with MPA and zone classes in a simple and globally applicable way. Applying both the IUCN categories and the regulation based classes will increase transparency when assessing marine conservation goals.
- Age and growth of megrim, Lepidorhombus boscii, Risso of the portuguese continental coastPublication . Castilho, Rita; Dinis, Maria Teresa; Erzini, KarimThe first study of age and growth of four-spotted scaldfish, more commonly known as megrim (Lepidorhombus boscii, Risso), an important (by catch ) species of the Portuguese trawl fishery from the Atlantic coast is presented. The analysis was based on data obtained from a total of 609 specimens sampled between 1985 and 1986. Otoliths were used for age determination. The Von Bertalanf~, growth parameters were estimated using the non-linear fitting method: Lt (females)=440[ 1 -e -°-14(t+ 1.32) ] and Lt= 375 [ 1 -e -°~4(t+ 1.93) ] for males. L~ and to values are significantly different. The megrim grows allometrically (slope of length-weight regressions > 3 ). Females live longer and gain weight at a faster rate than males. Differences in growth between sexes become more apparent from the second year onwards.
- Age and growth of Ray's bream (Brama brama) from the south of PortugalPublication . Lobo, C.; Erzini, KarimAge and growth of 234 Brama brama Bonnaterre (1788) (Pisces: Bramidae) caught hy semi-pelagic longline off the south coast of Portugal (Algarve) was studied using otoliths for age determination. Samples consisted of fish varying in total length from 32 to 56 cm and in weight from 332 to 2032 g. Age classes from III to XII were represented in the catches. The von Bertalanffy growth curve was fitted and the length/weight relationship was calculated. (C) 2001 Elsevier Science B.V. All rights reserved.
- 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 countsPublication . Fernandez-Carvalho, Joana; Coelho, Rui; Erzini, Karim; Santos, Miguel NevesThe 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 L(0), and a modified VBGF using a fixed L(0) 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: L(inf) = 293 cm FL, k = 0.06 y(-1) and L(0) = 111 cm FL for females; L(inf) = 206 cm FL, k = 0.18 y(-1) and L(0) = 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 bigeye thresher shark, Alopias superciliosus, from the pelagic longline fisheries in the tropical northeastern Atlantic Ocean, determined by vertebral band countsPublication . Fernandez-Carvalho, Joana; Coelho, Rui; Erzini, Karim; Santos, Miguel N.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 A. supercilious 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 = 293cm FL, k =0.06/yr and L0 = 111 cm FL for females; Linf = 206 cm FL, k = 0.18/yr 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 undulate ray, Raja undulata, in the Algarve (southern Portugal)Publication . Coelho, Rui; Erzini, KarimAspects of the population dynamics of the undulate ray, Raja undulata (Chondrichthyes: Rajidae), one of the more abundant elasmobranch fish captured along the Portuguese south coast (Algarve), were studied for the first time. Some traditional elasmobranch vertebral enhancing techniques were compared and the most precise for this species determined to be the cedar wood oil immersion and the alizarin red S stain. The sample consisted of 14 age-classes, with age-classes 3 to 8 being the most represented. Evidence of an annual deposition pattern of a pair of bands (one opaque and one translucent) was found by marginal increment analyses. Von Bertalanffy growth parameters were estimated and no differences found between males and females (all data: L-inf=110.22 cm, K=0.11 y(-1) and t(0)=-1.58 y).