Fishing Intensity Research Articles

Marine Protected Areas: reserve effect or natural variability? The Patagonian octopus case

Population characteristics can be influenced by specific factors of the habitat and the natural variability of populations can confuse the effect related to protected environments. This study compares the demographic characteristics of Octopus tehuelchus in three coastal environments: two Marine Protected Areas (San Antonio Bay (SAB) and Islote Lobos (IL)) and a traditional fishing zone (El Fuerte (EF)). Weight–frequency distributions, sex-ratio and recruitment were monthly compared between the three intertidal zones. Octopus tehuelchus was smaller in IL, where fishing intensity is lower or null, and reached the largest sizes in the main fishing area of EF and within SAB (where there is no regulation and a mid–high fishing intensity). The sex proportion in SAB and EF was 1:1 all along the year. Although the proportion of mature females in IL was higher, the highest recruitment was observed in EF (the traditional fishing ground). These new data suggest that previous studies, which reported that Marine Protected Areas have positive effects for O. tehuelchus populations, can no longer be supported, and highlight the importance of understanding and quantifying the magnitude and range of natural variability in each environment when assessing the effectiveness of Marine Protected Areas.

Fishing intensity metrics for use in overfishing determination

Abstract Cordue, P. L. 2012. Fishing intensity metrics for use in overfishing determination. – ICES Journal of Marine Science, 69: 615–623. The issue of constructing a technically correct fishing intensity metric from the output of a stock assessment model is considered. Four metrics of annual overall “fishing intensity” are defined. The metrics are applicable to age- or length-structured stock assessment models, which may, or may not, include complex spatial and temporal structure in the population and the fisheries. Two of the metrics are termed “direct” as they are calculated from the model output in the given year. Equivalent annual U is a number-based exploitation rate, and equivalent annual F is an average fishing mortality rate. The other two metrics, equilibrium stock depletion (ESD) and spawning potential ratio (SPR), measure fishing intensity in terms of the potential long-term effect on the stock (via 1–ESD and 1–SPR). The use of the metrics for overfishing determination is illustrated with a simple, spatial, two-fishery model. Summary statistics, which are sometimes used as a measure of fishing intensity, such as total catch over a reference biomass, or a number-weighted F are shown to be technically invalid for overfishing determination. The common approach, for virtual population analysis assessments, of using an average F over a specified age range is also discussed.

A Trawl Disturbance Indicator to quantify large scale fishing impact on benthic ecosystems

We evaluated the adequacy of an indicator of benthic community health to assess trawling disturbance by sampling epifauna at 6 sites subjected to variable fishing intensity in the Mediterranean: from no fishing, in an area associated to a marine reserve, to high fishing intensity, in trawling grounds. The proposed indicator is based on the biological traits composition of epifaunal species that determine vulnerability to trawling: mobility, fragility, position on substrata, average size and feeding mode. Five groups defined by the combination of these biological traits represented different levels of vulnerability to trawling. Results based on analysis of the relative abundance of these groups at each site showed that the biological traits significantly reflected ecosystem disturbance, with the less disturbed communities having the highest abundance of groups considered vulnerable to trawling. According to these findings a Trawl Disturbance Index (TDI) was proposed as a tool for fisheries managers to assess the ecosystem health.

Studies on ecological characteristics variation and population dynamics of four lizardfishes in the southern Taiwan Straits

The ecological characteristics of four lizardfishes, Trachinocephalus myops, Saurida undosquamis, Saurida tumbil and Saurida elongata, were studied from specimens (910 T. myops, 454 S. undosquamis, 686 S. tumbil and 744 S. elongata) collected monthly in the southern Taiwan Straits from April 2005 to March 2006. The population dynamics of the four lizardfishes was also discussed by the comparison with the previous studies. All being composed of 7 a classes; the dominant group of T. myops and S. tumbil was 1–2 a, while S. undosquamis and S. elongate were 2–3 a. The total mortality coefficient Z and the fishing mortality F were at high as indicated by the exploitation ratio E(>0.5), and a large number of by-caught juvenile and young fishes showing that the stock of lizardfishes in this area was overexploited and the fishing gear was irrational. Compared with the previous studies, the maximum and mean fork length, body mass and age of the four lizardfishes declined gradually, the lizardfishes populations were younger in age and smaller in size. The asymptotic fork length L∞ decreased while increasing growth coefficient k, and age at the inflexion point of mass tr was younger compared with the previous studies. The declining of older ones has moderated the feeding competition and the younger ones grew faster. The larger mortality parameters Z,M and F have revealed higher fishing pressure. The smaller change of the first mature fork length of female T. myops and the change from K selection pattern to r selection pattern of S. tumbil have indicated a more vulnerable fishery ecosystem in this area. The changes of ecological characteristics and population dynamics may be caused by over-exploitation of demersal fishes such as the lizardfishes, especially a large number of juvenile and young fishes by-catch by the current fishing gears and methods. Therefore, in addition to the traditional fishery management approach such as the minimum length-limit, ecosystem approach to fisheries management (EAF) should be taken to improve the practical marine ecosystem management, including increased fishing intensity of the non-economic species especially the feeding competitors of the lizardfishes and the conservation of the pelagic fishery population in the fisheries ecosystem, in order to restore the fishery population and achieve the sustainable use of the fishery stocks.

Prevalence and intensity of internal parasitic helminthes infected black sole fish, Brachirus orientalis (Bloch and Schneider, 1801) in the Persian Gulf.

This study was conducted to identify intestinal helminthes parasites. The helminthes fauna is collected from body cavity and intestines of 108 specimens of Brachirus orientalis which were obtained from Abadan port (waterfront) and investigated during the years 2009-2010. Most of the 4 species of helminthes were found in the intestine and body cavity of the examined fishes. The helminthes found was composed of 2 digenetic Trematodes (Lepocreadioides zebrine, Allocreadium brachirusii) all adults, in the intestine. The general prevalence of Lepocreadioides zebrini and Allocreadium sp. was in the intestine, 58% and 73% respectively, nematode Hysterothylacium aduncum with a prevalence of 23% was the only cestod Protocephalus sp. with 16%, except Pterobothrium sp., which was reported previously. Most parasite species found in this study have been reported for the first time from Iran and Allocreadium sp. is introduced as a new species and described here.

PENDUGAAN POTENSI SUMBERDAYA PERIKANAN LAUT DAN TINGKAT KERAGAAN EKONOMI PENANGKAPAN IKAN (KASUS DI TPI SENDANG BIRU KABUPATEN MALANG)


 
 The Increased fishing intensity will provide positive and negative impacts. Positive impact is an increase in production that can provide benefits, while the negative impact is eventually decline in production catches. The purpose of this research is potential of Estimating Maximum Sustainable Yield (MSY) in Malang Regency could still be maintained. MSY at the level of Maximum Economic Yield (MEY). Optimization of fishing effort and analysis economic eligibility fishing effort. The method of research using the survey method, Analysis of the data used is static Bio-economic model, and Gorden-Schaefer model. While the research results obtained MEY value of 5,789,952. kg/year and the actual conditions, a production of 5,221,781 kg/year and MSY of 5,829,206 kg/year, the rate of 90% utilization optimization, and optimal fishing levels have exceeded MSY. The advantage of fishermen in biology and economics as much as 5,789,952 kg/year. Conclusion The results showed that the water condition in Malang Regency was not economically efficient, because already there is excess fishing effort. Optimization needs to be done by limiting fishing effort, intensified fishing activities in deeper waters.
 
 

Elasmobranch spatial segregation in the western Mediterranean

Basic information on the distribution and habitat preferences of ecologically important species is essential for their management and protection. This study focuses on the depth related trends and the geographic patterns that shape the community of the elasmobranch species in the Balearic Islands (Mediterranean Sea) using data collected from 2001 to 2009. Non-metric Multi-Dimensional Scaling (MDS) ordination was used to detect zonation patterns in the community. Generalized Additive Models (GAMs) were applied to analyse spatial and temporal variation in elasmobranch community descriptors (abundance, biomass, mean fish weight, number of species and diversity), as well as the abundance and mean length of the four individual species (S. canicula, G. melastomus, R. clavata, R. miraletus). Depth was the main factor determining the assemblage composition, and the MDS analysis identified four main groups with 60% of the similarity found to correspond to the continental shelf, shelf break, upper slope and middle slope of the surveyed area. GAM analysis identified spatial patterns that were independent of the bathymetric distribution preference. Although depth was a strong predictor for all the analyses performed, the geographic variation in the elasmobranch abundance was also important. The results also show a reduction in the mean length of the elasmobranch species in the areas with high fishing intensity. Our study evidences a clear spatial segregation of the main species throughout the ontogeny because the geographic and bathymetric effects were highly size dependent, with clear differences between the bathymetric distributions of juveniles and adults but no clear spatial overlapping. This study sheds new light on the spatial distribution of the elasmobranch species off the Balearic Islands, which is essential information for protecting marine organisms along with their habitats and promoting ecosystem based management.

Robustness of egg production methods as a fishery independent alternative to assess the Eastern Baltic cod stock (Gadus morhua callarias L.)

At present, several cod stocks are outside safe biological limits and are managed under recovery plans. For these stocks Total Allowable Catches (TAC's) are generally low and quotas are accompanied by a broad variety of technical measures influencing the fishing patterns. Consequently, the input data to stock assessment models relying on catch statistics from the commercial fisheries is potentially biased and the perception of stock status may be incorrect. Egg production methods (EPM) provide a fishery independent alternative. Additionally, they provide better estimates of stock reproductive potential (SRP). Eastern Baltic cod (Gadus morhua callarias L.) has severely declined throughout the 2nd half of the 1980s and 1st half of the 1990s due to climate-driven adverse hydrographic conditions and high fishing intensity. Since 2007 the stock is managed under a long-term management plan and showed signs of recovery in most recent years. Since 1986, egg surveys have been carried out regularly in the Bornholm Basin, the most important spawning area of Eastern Baltic cod since mid-1980s. In the present paper the robustness of EPM towards simplification of spawning parameters and towards reduction of the number of egg surveys is tested applying three different methods requiring different numbers of egg surveys. We applied the annual egg production method (AEPM) requiring full egg survey coverage of the spawning season to estimate cod abundances in the Bornholm Basin. In addition, the daily fecundity reduction method (DFRM) and the daily egg production method (DEPM) were tested, the latter two methods requiring only single egg surveys, but require more complex reproduction input parameters. All three methods provided a comparable result, which was also expected as many spawning parameters were derived from the same underlying data sets. In a sensitivity analysis several input parameters were varied simultaneously up to 20% in both directions. EPM were especially sensitive towards changes in proportions of mature females at age, whereas changes in the various fecundity parameters and spawning fraction were less influential.EPM results followed the large scale spawning stock trends of the Baltic International Trawl Survey index, whereas the year to year variations of the index were not captured to well. EPM yielded spawning stock sizes in the same order of magnitude as provided by a spatially down-scaled multi-species stock assessment model.

Parasite community structure of cod from Bear Island (Barents Sea) and Pomeranian Bay (Baltic Sea)

Parasite community structure of cod from Bear Island (Barents Sea) and Pomeranian Bay (Baltic Sea) A total of 142 cods: 60 from the South-East Ground of Bear Island and 82 from the Pomeranian Bay (Baltic Sea) were examined for their ecto- and endoparasites. Twenty different parasite species, comprising one Myxosporea, three Cestoda, four Digenea, seven Nematoda, three Acanthocephala and two Crustacea were found. The parasite component communities comprised 1446 individuals (17 species, six higher taxa) from the Bear Island and 6588 individuals (nine species, three higher taxa) from Pomeranian Bay. The observed parasite host specificity was low, and the intensity in a single fish ranged from one to 279 specimens. The eudominant parasite species were Echinorhynchus gadi, Hemiurus levinseni and Contracaecum osculatum. The dominant parasite communities from the Bear Island were nematodes, but acanthocephalans dominated in cod from the Baltic Sea. It appears that one group of parasites, better adapted for the specific conditions of the macrohabitat, has replaced another. The most prevalent parasites were E. gadi, Anisakis simplex, C. osculatum and Hysterothylacium aduncum, and the mean values of crowding were the highest for E. gadi and Pomphorhynchus laevis. The nematode Camallanus lacustris was noted in this host species for the first time. Only six species of parasites were common to cod from both fishing grounds.

Selection of the mesh size of control codend in analysis of size selectivity of multi-codends beam trawls

In comparative fishing method,one of important experimental methods in research on size selectivity of trawls,the control codend mesh size is crucial and a possible upper limit is generally suggested to be half the mesh size of the test codend. However,the suggestion is unavailable when the body size of target specie of trawl is small enough,especially in shrimp or prawn trawl fisheries. In order to discuss how to choose a rational mesh size of control codend,experiments,in which test codends with different mesh sizes (20,30,35 and 40 mm) were rigged in a same multi-codends beam trawl and fished simultaneously,were carried out in Lvsi Fishing Ground. The catch frequency of Parapenaeposis hardwickii,Pseudosciaena polyactis and Collichthys lucida retained by codends were fitted to a selectivity analysis model in which the selectivity curves of different codends were regarded as geometrical similar under two contrary hypotheses (hypothesis 1:the 20 mm mesh size codend is regarded as test codend and selective for catch species and,hypotheses 2:as control codend and non-selective for species). The result demonstrated that the goodness of model fit and the selective parameters of different test codends were not affected significantly by the two contrary hypotheses. Taking the difference in relative fishing intensity and statistical method of analyzing size selection between multi-conends trawl and conventional trawls into account,authors suggest that the assumption of non-selectivity of 20 mm mesh size control codend is acceptable in analysis of size selectivity in the experiemts,which means that the general upper limit of control codend mesh size could be broken.

Spatial patterns of fishing effort off San Diego: implications for zonal management and ecosystem function.

The essence of ecosystem-based management is managing human practices to conserve the ecosystem. Ecologists focus on understanding the ecosystem, but there are fundamental information gaps including patterns of human exploitation. In particular, the spatial distribution of fishing effort must be known at the scales needed for ecologically relevant management. Fishing is a primary impact on coastal ecosystems, yet catch distribution at scales relevant to habitats and processes are not well known for many fisheries. Here we utilized photographic time series, logbook records, and angler surveys to estimate the intensity and spatial pattern of commercial and recreational fishing. Effort was clearly aggregated for most types of fishing, the motivating factors for effort distribution varied among areas, and effort was coupled or uncoupled to habitat depending on the area and type of fishing. We estimated that approximately 60% and approximately 74% of private recreational and recreational charter vessel fishing effort, respectively, were concentrated into two small areas that also included approximately 78% of commercial sea urchin effort. Exploitation and effort were considerably greater in one kelp forest, which has important implications for patterns of kelp persistence, productivity, and ecosystem function. Areas subject to the greatest recreational fishing pressure appeared to have lower diversity. Our results indicate that fine-scale patterns of fishing effort and exploitation have profound consequences for ecosystem functioning and biodiversity. 'Ecosystem-based management of nearshore ecosystems depends on an understanding of the fine-scale patterns of exploitation.

Characteristics of Marine Recreational Fishing in the anakkale Strait (Turkey)

The economic and harvest impacts of Marine Recreational Fishing (MRF) in Çanakkale Strait were analysed along with fishing policy, sociology and habits of fishers. Data sources included field survey data carried out along the entire length of the Çanakkale strait and policy information gathered from published sources. MRF policy is commendable, even in the fishing tourism sector, and is better developed than that in many other European countries. In Çanakkale, 9.9% of the population is recreational fishers. Recreational fishers are typically men (90%), primarily those between the ages of 25 and 49 yrs. The occupation of the recreational fishers ranged from self-employed (28%), students (28%), retired persons (22%) and public employees (15%), to currently-unemployed persons (7%). An analysis of diel behaviour showed that most recreational fishers preferred fishing during the day (56.1%), while the evening was the next most preferred time for fishing (18%), followed by the night-time (9.8%), while a substantial number of recreational fishers (16.1%) reported that they fished at any time of day. The most popular type of fishing was shore-based (68%), followed by boat-based (21%), and underwater fishing (11%). The mean daily fishing times were 6.07 h d-1, 6.18 h d-1 4.75 d-1 for boat-based, underwater and shore-based fishing, respectively. Summer and autumn were the preferred seasons for shore-based and underwater fishing, while autumn and winter were preferred for boat-based fishing. The highest Catch per Unit Effort (CPUE) was observed for boat-based fishing (2.77 kg h-1), followed by underwater (0.97 kg h-1) and shore-based fishing (0.81 kg h-1). The catch composition included 51 species, though the catch composition of each fishing type was mostly comprised of only 3 or 4 species. The impact of the MRF harvest was high (30% of commercial fishing), particularly for bluefish (Pomatomus saltatrix) and picarel (Spicara smaris) species. The economic impact of MRF was highly negative. Several indicators including the following revealed a high percentage of trading catch (47%) being conducted under the guise of a recreational label: annual fishing intensity, total costs, target species, and sales. At present, it is evident that the highly developed recreational fishing policy in Turkey is not sufficient to ensure that recreational fishing is sustainable or to prevent fishing conflicts in Turkey. This study revealed the need for establishing monitoring, control and surveillance programs to ensure the sustainability of fish resources and fisheries including MRF.

An index to assess the risk to stony corals from bottom trawling on seamounts

AbstractStony (scleractinian) corals are common on seamounts and can form extensive reef‐like structures which in turn provide important habitat for associated species. Aggregations of fish also occur on seamounts, which in recent decades have become the target of commercial bottom trawl fisheries that have damaging impacts on benthic communities. Such fisheries occur throughout the world’s oceans, and the majority are located on seamounts about which little is known of their biodiversity or likely fisheries impact. Here we develop an index of risk for stony corals on seamount summits. The index combines a metric of vulnerability measured by the coincidence of seamount summits, target fish ranges and likelihood of coral presence with an assessment of likely fisheries impact derived from a fishing intensity effects study and fishing effort‐catch data. We provide spatial maps depicting the locations of vulnerable seamount features, and those at particular risk to bottom trawling. Application of the risk index may help to provide guidance to fisheries or environmental managers faced with balancing fisheries management and habitat conservation.

Recovery of UK seabed habitats from benthic fishing and aggregate extraction—towards a cumulative impact assessment

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 411:259-270 (2010) - DOI: https://doi.org/10.3354/meps08662 Recovery of UK seabed habitats from benthic fishing and aggregate extraction—towards a cumulative impact assessment Jo Foden1,*, Stuart I. Rogers2, Andrew P. Jones1 1School of Environmental Sciences, University of East Anglia, Norwich, Norfolk NR4 7TJ, UK 2Centre for Environment, Fisheries and Aquaculture Science (Cefas), Pakefield Road, Lowestoft, Suffolk NR33 0HT, UK *Email: jo.m.foden@uea.ac.uk ABSTRACT: Assessing cumulative impacts of multiple pressures on the marine environment can help inform management response. This requires understanding of the spatial and temporal distribution of human pressures and their impacts. Quantifying seabed recovery rates from 2 significant pressures in European waters, benthic fishing and aggregate extraction, is a significant step towards assessing sensitivity and cumulative impacts. Vessel monitoring system data were used to estimate the distribution and intensity of benthic fishing in UK (England and Wales) marine waters (2006 to 2007). Data were separated by towed bottom-fishing gears (scallop dredges, beam and otter trawls) and linked to habitat in a geographic information system. Recovery periods of seabed habitats were estimated by literature review, for gear types and fishing intensity. Recovery rates generally increased with sediment hardness, and habitats required longer periods of recovery from scallop dredging than from otter or beam trawling. Fishing pressure across the habitat–gear combinations was such that 80% of the bottom-fished area was estimated to be able to recover completely before repeat trawling, based on mean annual trawl frequencies. However, in 19% of the UK’s bottom-fished seabed, scallop dredging in sand and gravel and otter trawling in muddy sand and reef habitats occurred at frequencies that prevented full habitat recovery. In 2007, benthic fishing and aggregate extraction occurred together in an estimated 40 km2 (<0.02%) of the UK seabed. Cumulative impacts were estimated as total recovery time under 4 scenarios: greatest, additive, antagonistic and synergistic impacts. Recovery from aggregate extraction required much greater periods than from benthic fishing, and gravel was identified as a more sensitive habitat than sand. KEY WORDS: Towed bottom-fishing · Recovery · Cumulative effects · Fishing intensity · Marine habitats · Aggregate extraction · UK seabed · Vessel monitoring system Full text in pdf format PreviousNextCite this article as: Foden J, Rogers SI, Jones AP (2010) Recovery of UK seabed habitats from benthic fishing and aggregate extraction—towards a cumulative impact assessment. Mar Ecol Prog Ser 411:259-270. https://doi.org/10.3354/meps08662 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 411. Online publication date: July 29, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Dynamics of structural parameters of populations of the bream Abramis brama (Cyprinidae) in Rybinsk Reservoir in 1954–2007

The data on age, size, and sex structure of the population, on the linear and weight growth of bream Abramis brama are generalized for the period of 1954–2007 in Rybinsk Reservoir. Analysis of dynamics of these parameters demonstrated that recently a high fishing intensity is both reflected on the size of the stock but also determines the changes in structural parameters of the bream population. At present, in the exploited stock of bream, the specimens of junior ages dominate. The part of specimens older than ten years, which previously made the bulk of catches, now compose not more than 10–15%. This resulted in a rather noticeable decrease of mean age and size in catches. The previously observed sex ratio, near 1: 1, shifted towards a significant prevalence of males. The age of the first spawning and of the fish spawning for the first time decreased. These changes indicate that the fishing load surpasses adaptational potential of bream.

An agro-ecological evaluation of aquaculture integration into farming systems of the Mekong Delta

This study compared ecological sustainability of Integrated Agriculture-Aquaculture (IAA) systems with different forms and intensity of aquaculture integration in the Mekong Delta of Vietnam: orchard-based and low-input fish (O-LF); rice-based and medium-input fish (R-MF); and rice-based and high-input fish (R-HF) farming systems. We monitored eleven IAA-farms from September 2002 to September 2004. ECOPATH models, based on nitrogen flows, produced 19 agro-ecological system attributes that were reduced to four factors by factor analysis (Productivity-Efficiency; Diversity; Maturity; Aquaculture Integration), explaining 76.8% of total variance. In general, R-HF farms scored higher on Productivity-Efficiency, R-MF on Diversity, and O-LF farms on Maturity than the other systems. Within all three farm systems, variability among farms was high, caused by differences in land use, financial and crop disease constraints, market possibilities, and family conditions. The ponds and ditches served as a trap to capture nutrients and re-distribute them to other parts of the farms. Despite the differences in intensity of fish keeping between the three systems, the fish ponds in the rice-based systems and fish in ditches in the orchard-based system contributed to the same extent to the nutrient supply of other components. Differences in nutrient efficiency among the farming systems were caused primarily by the inefficient orchard and rice components on the O-LF farms. Fertilizers were often applied in excess. Nutrient use efficiency should be improved through proper application of fertilizers and promotion of the traditional integration practices.

Environmental and fishing effects on the abundance, size and sex ratio of the blue‐throated wrasse, Notolabrus tetricus, on South Australian coastal reefs

Abstract The blue‐throated wrasse, Notolabrus tetricus (Richardson), is a site‐attached protogynous hermaphroditic species, with a small home range of 1000–2000 m2, and the most abundant fish on inshore coastal reefs of South Australia. Long‐term studies over 18–24 years were conducted at an island reserve site and a fished mainland reference site. At the reserve site the retention rate of fish (reduced by mortality + emigration) was directly correlated with female mean size; the female:male sex ratio ranged from 10 to 20:1, consistent with an induction‐inhibition model of sex‐change. At the fished reference site, female mean size declined under intense fishing, and the sex ratio became strongly skewed towards females. Additional spatial surveys over &gt;2000 km of coast showed that: (1) juvenile and adult abundance was variously determined by habitat features, such as substratum‐type, depth, bottom relief, wave exposure and algal canopy cover, and by geographical factors, such as distance off‐shore and within gulfs; and (2) that female mean size and the sex ratio were strongly influenced by recreational fishing, and to a small extent by bottom relief and other factors. The results suggest that female mean size and the sex ratio together can be used as an indicator of recreational fishing intensity at local scales. As populations of sequential hermaphroditic species are sensitive to size‐selective harvesting, management measures should aim to prevent sperm limitation, reproductive failure and skewed sex ratios in this species.

Spatial patterns of fishing effort off San Diego: Implications for zonal management and ecosystem function

The essence of ecosystem-based management is managing human practices to conserve the ecosystem. Ecologists focus on understanding the ecosystem, but there are fundamental information gaps including patterns of human exploitation. In particular, the spatial distribution of fishing effort must be known at the scales needed for ecologically relevant management. Fishing is a primary impact on coastal ecosystems, yet catch distribution at scales relevant to habitats and processes are not well known for many fisheries. Here we utilized photographic time series, logbook records, and angler surveys to estimate the intensity and spatial pattern of commercial and recreational fishing. Effort was clearly aggregated for most types of fishing, the motivating factors for effort distribution varied among areas, and effort was coupled or uncoupled to habitat depending on the area and type of fishing. We estimated that ∼60% and ∼74% of private recreational and recreational charter vessel fishing effort, respectively, were concentrated into two small areas that also included ∼78% of commercial sea urchin effort. Exploitation and effort were considerably greater in one kelp forest, which has important implications for patterns of kelp persistence, productivity, and ecosystem function. Areas subject to the greatest recreational fishing pressure appeared to have lower diversity. Our results indicate that fine-scale patterns of fishing effort and exploitation have profound consequences for ecosystem functioning and biodiversity. Ecosystem-based management of nearshore ecosystems depends on an understanding of the fine-scale patterns of exploitation.

Megabenthic diversity patterns and community structure of the Blanes submarine canyon and adjacent slope in the Northwestern Mediterranean: a human overprint?

AbstractThe composition and structure of megabenthic communities in the Blanes canyon and adjacent open margin (Northwestern Mediterranean) were studied. The aim was to assess the effect of the canyon and commercial fishing intensity on the community composition and structure of benthic megafauna by (i) describing the megabenthic community composition, (ii) quantifying faunal abundance and biomass and (iii) describing community structure with MDS analyses and biodiversity indices. The results are compared between three sites (canyon head, canyon wall and open margin) located between 435 m and 700 m. Samples were collected using a commercial bottom trawl between April 2003 and March 2004. These sites are exploited by the local fishing fleet that targets the rose shrimp Aristeus antennatus. A total of 131 megabenthic species were identified from the three sites, with fishes and decapod crustaceans being the most speciose, most abundant and of higher biomass. The species richness, abundance and biomass of non‐crustacean invertebrates were low. There were no significant differences in total abundance and biomass between the three sites. However, community structure analysis suggests that the open margin community is significantly different from the canyon head and canyon wall, with a lower species richness, lower diversity and lower evenness. The open margin community also reflects a higher degree of disturbance compared to the two canyon habitats. The results indicate that there is a canyon effect on the community structure of benthic megafauna, but this may be modulated by differing fishing pressure, which adds an additional factor to margin heterogeneity.

Life history change in commercially exploited fish stocks: an analysis of trends across studies.

Age and size at maturation have declined dramatically in many commercial fish stocks over the past few decades – changes that have been widely attributed to fishing pressure. We performed an analysis of such trends across multiple studies, to test for the consistency of life history changes under fishing, and for their association with the intensity of exploitation (fishing mortality rate). We analyzed 143 time series from 37 commercial fish stocks, the majority of which originated from the North Atlantic. Rates of phenotypic change were calculated for two traditional maturation indices (length and age at 50% maturity), as well as for probabilistic maturation reaction norms (PMRNs). We found that all three indices declined in heavily exploited populations, and at a rate that was strongly correlated with the intensity of fishing (for length at 50% maturity and PMRNs). These results support previous assertions that fishing pressure is playing a major role in the life history changes observed in commercial fish stocks. Rates of change were as strong for PMRNs as for age and size at 50% maturity, which is consistent with the hypothesis that fishing-induced phenotypic changes can sometimes have a genetic basis.