Mean CPUE Research Articles

Changes in Relative Abundance of Several Minnesota Fishes from 1970 to 2013

AbstractLarge‐scale ecological stressors such as climate change, habitat degradation, and invasive species increasingly affect fisheries across watershed or political boundaries within which they are typically managed. Though broad‐scale analyses of trends in fish populations and changes in aquatic communities can be useful for detecting the effects of these stressors, they are rarely possible due to a lack of long‐term data sets. The Minnesota Department of Natural Resources has used gill nets and trap nets to monitor fish communities in lakes since 1940, and the techniques have been standardized since 1970. We applied a random‐coefficient mixed‐effects model to mean CPUE data to describe statewide and local population trends of eight key fish species (Black Crappie Pomoxis nigromaculatus, Bluegill Lepomis macrochirus, Largemouth Bass Micropterus salmoides, Northern Pike Esox lucius, Smallmouth Bass M. dolomieu, Walleye Sander vitreus, White Sucker Catostomus commersonii, and Yellow Perch Perca flavescens) sampled from 1970 to 2013 in 119–1,499 lakes. We found increasing statewide trends in gill‐net CPUE of Black Crappie, Bluegill, Largemouth Bass, Smallmouth Bass, Northern Pike, and Walleye and decreasing trends for Yellow Perch and White Sucker. Statewide trends in average trap‐net CPUE were positive for Bluegill, negative for Black Crappie, Walleye, White Sucker, and Yellow Perch, and stable for Largemouth Bass, Northern Pike, and Smallmouth Bass. We compared the CPUE trends across lake types developed for Minnesota lakes and found some differences, especially in medium and large mesotrophic lakes, suggesting that some species display changes in abundance more in those lakes types than in others. This study quantifies temporal changes in Minnesota's fish community structure and can help managers focus future research and management activities in the state and in similar waters across central North America.Received May 14, 2014; accepted September 9, 2014

Captura de tiburones en la region noroccidental de Cuba

Sharks have been important as seafood source and fisheries revenue in Cuba. Nevertheless, current information about this group of fishes in Cuba is scarce and in the last decades they have not been the focus of any organized research. From October 2009 to June 2011, fisheries and biological (229 sharks examined) data were collected at four landing sites in the northwest of Cuba. At present, there is no organized fishery specifically targeting only sharks along the northwest coast of Cuba, but they are caught as a component of multispecies fisheries on the insular shelf and as bycatch in longline fisheries targeting billfishes. We registered a total of 17 species, six in the commercial fishery, dominated by Carcharhinus perezii, Sphyrna mokarran, and Carcharhinus leucas, and 14 in the sport fishery (i.e., small-scale artisanal, not recreational properly), dominated by Isurus oxyrinchus, Isurus paucus, Carcharhinus longimanus, Carcharhinus falciformis, Galeocerdo cuvier and Prionace glauca. Mean CPUE by months in sport fishing varied from 0.43 to 4.44 number of sharks caught per ten fishing trips. Most oceanic sharks caught in the Cuban sport fisheries are highly migratory species and their populations show great ecological connectivity throughout the Gulf of Mexico and adjacent waters. This fact and the presence of a high proportion of individuals of C. longimanus and C. falciformis below maturity size are important results to be considered for regional conservation of sharks and planning rational use of shark fisheries.

The Effect of Seasonal Changes on Freshwater Fish Assemblages and Environmental Factors in Bukit Merah Reservoir (Malaysia)

Abstract Seasonal changes of freshwater fish assemblages and environmental factors in Bukit Merah Reservoir were carried out from January-February 2013 (dry season) to March-April 2013 (wet season) by measuring several physico-chemical parameters such as dissolved oxygen (DO), water temperature, pH, water conductivity, total dissolved solids (TDS) and water clarity. 19 fish species comprising of 10 families were collected by using experimental gill nets with different mesh sizes at four different sampling stations. Mean CPUE for total catch and biomass were significantly different between dry and wet season (p < 0.05). Based on a T-test analysis, water temperature, pH and conductivity were significantly different (p < 0.05) between seasons whereas a one-way ANOVA displayed a significant difference in TDS and water clarity between sampling stations (p < 0.05), implicating that those factors did not give major influence towards other parameters in a man-made reservoir. From all fish species studied, only mean CPUE for individuals (CPUEn) of Osteochilus vittatus and Oxygaster anomalura had a significant difference between seasons (p < 0.05); probably an indicator of their migration season

Sea-bob shrimp in Bahia state: aspects of their fishing and biology

The fishing activity Bahia presents great economic importance, being basically artisanal. Trawling is carried out since the 70’s, and among the resources exploited, the-bob-shrimp ( Xiphopeneus kroyeri ) is the most important. We analyzed data of its fisheries production (2001 and 2007), and presented aspects of their biology to the south coast (LS) and southernmost (LES). For assessment of fish production data were compiled from statistical bulletins CEPENE / IBAMA for the biological data used were generated between the years 2003/2005 and 2010/2011 for the coast of Ilheus (LS) and 2004/2009 for the RESEX (LES). The species represented half of shrimp harvested, although the composition was not homogeneous along the coast, which may represent up to 90% of the fisheries in the south coast and southern end. In Ilheus, there was a significant decline in mean CPUE between the first (2.60 ± 2.40 kg h-1) and the second period (0.73 ± 1.41 kg h-1), being the amount recorded in RESEX Corumbau about four times higher (9.96 ± 8.29 kg h-1). In both locations, the lowest catches occurred in the summer, with periods reproductive and recruitment continued. These results may be associated with different management strategies applied on both sites. We suggest that a standardized of landing data collection and a continuous monitoring by the responsible agencies are necessary; that the management policy and legislative currently in place should be reassessed and that new public policies that facilitate the management of this resource need to be developed.

Investigations on juvenile fish excluder cum shrimp sorting device (JFE-SSD)

Penaeid shrimp is a major resource in India contributing about 7.4% of the total marine fish landings. They are mostly landed by small mechanized trawlers. Shrimp trawling generates large quantities of bycatch mostly consisting of juvenile fishes, due to use of small mesh size in codends of trawl nets. Juvenile Fish Excluder cum Shrimp Sorting Device (JFE-SSD) is a bycatch reduction device with an in situ sorting mechanism, which replaces the conventional codend in a trawl. The device was designed to catch shrimps and commercially important fish species using a specially designed oval sorting grid with appropriate bar spacing and dual codends. Shrimp sorting efficiency and bycatch exclusion characteristics of JFE-SSD attached to a 29.6 m shrimp trawl, was tested by experimental fishing along the coastal waters off Cochin, India. Out of a total of 317.07 kg of catch encountered in the JFE-SSD installed trawl, 58.22% was retained in lower codend, 17.53% in upper codend and 24.25%, mostly consisting of juveniles and sub-adults of finfishes and shellfishes, was excluded from upper codend. The mean CPUE registered for upper and lower codend were 7.23±1.04 SE and 5.84±0.96 SE kg h-1 respectively. The CPUE of shrimps retained in upper and lower codends were significantly different (Kruskal-Wallis test (1,62), P<0.001), but the mean CPUE for fishes did not vary significantly. The average escapement of shrimps and juvenile fishes from upper codend were 0.06±0.02 SE kg h-1 and 2.40±0.44 SE kg h-1 respectively. Significant differences in the length composition between upper and lower codends were noticed for Megalaspis cordyla, Stolephorus waitei, Metapenaeus dobsoni and Parapenaeopsis stylifera. The experiments demonstrated in situ sorting ability of the device and its potential to reduce the bycatch of juveniles and sub-adults in shrimp trawls.

Analysis of artisanal fisheries in two reservoirs of the upper Paraná River basin (Southeastern Brazil)

We compared the artisanal fisheries, in terms of catch strategies, productivity, and gross per capita income, at two reservoirs: the Barra Bonita (an eutrophic reservoir with some introduced species), and the Jurumirim (an oligotrophic reservoir, with no introduced species). Published data and structured interviews with fishers were used to evaluate fishing activity, fish biomass, and the financial performance of the fisheries. In the Barra Bonita Reservoir we analysed data from 745 fishing trips, from which 86,691.9 kg of fish were landed, with a mean CPUE of 62.4 kg/fisher-1 day-1. The main type of fish caught was tilapia (71,513.5 kg; CPUE of 51.5 kg/fisher-1 day-1), which constituted 82.5% of the biomass caught. In the Jurumirim Reservoir, we analysed data from 2,401 fishing trips, from which 25,093.6 kg of fish were landed, with a mean CPUE of 10.4 kg/fisher-1 day-1. The main type of fish caught was "traíra" (6,158.6 kg; CPUE of 2.6 kg/fisher-1 day-1), which constituted 24.5% of the biomass caught. Ordination analysis (PCA) indicated that there was a difference in composition between the fishing reservoirs and ANCOVA showed that there was a significant difference in fish production between the reservoirs. A Student's t-test showed that fishers in the Barra Bonita Reservoir had a significantly higher gross per capita income than those from the Jurumirim Reservoir. Although the Barra Bonita Reservoir has a higher fish production and the fishers earn a higher gross per capita income, we recommend the Jurumirim Reservoir as a model for artisanal fishery management because fishing activity in this reservoir is viable in the long term and such a model would promote conservation and sustainability. This contrasts with the Barra Bonita Reservoir, in which the fishery is not viable in the long term, due to environmental problems caused by artificial eutrophication and the introduction of alien species. It is also noted that in many countries, management of fisheries based on exotic species has not been viable in the long term.

Fish sampling in the marine-dominated Kariega Estuary, South Africa, using a demersal otter trawl: day/night effects

Very few demersal fish assemblage studies using otter trawls in estuaries have been done in South Africa and none of these have tested for the effects of diel period. This study aimed to test whether diel period affects otter trawl catches in the clear, permanently open Kariega Estuary in terms of both species composition and abundance. Fish were sampled by day and night from 30 October to 1 November 2007 at 15 sites using an otter trawl. More species were collected at night, when there were higher catch rates for all key species, with the exception of Rhabdosargus holubi, which was more abundant during the day. Overall assemblages collected by day and by night were similar, with six species accounting for over 90% of the catch in both day and night samples. Both day and night samples reflected differences related to region, with the highest mean CPUE during day and night sampling being recorded in the head region.

Fethiye yöresinde (Akdeniz) pelajik Kılıç balığı paraketalarının av verimini arttırmak için kullanılan ışık çubukları üzerine denemeler

In this study, catch efficiency of light sticks on pelagic swordfish longline were studied. This study was carried out from September 20th of 2012 to December 31st of 2012 in Fethiye region and a total of 10 fishing operations were performed. All measurements were made on board. CPUE data of 50 swordfish that caught were compared in terms of total, lightened zone and dark zone. Mean CPUE was 131±22.72 kg/1000 hooks, CPUE of lightened zone was 352±61.32 kg/1000 hooks and CPUE of dark zone was 20±4.76 kg/1000 hooks. A total of 9 different species were caught during operations. The target species, Xiphias gladius had the highest ratio both in number (81.2%) followed by Muraena helena>Coryphaena hippurus≥Ruvettus pretiosus>Carcharhinus plumbeus≥ Lobotes surinamensis>Prionace glauca≥Alopias vulpinus ≥ Isurus oxyrinchus.

Evaluating the Performance of Vertical Longlines to Survey Reef Fish Populations in the Northern Gulf of Mexico

AbstractA common critique of many stock assessments is the lack of fishery‐independent abundance indices and age composition data. Such data streams are essential in evaluating population trajectories that are derived largely from harvest and age composition of landings. For example, high scientific uncertainty in the most recent stock assessment of Gulf of Mexico red snapper Lutjanus campechanus resulted from a conflict between trends in fishery‐dependent and fishery‐independent data. Because sample sizes for the latter data were an order of magnitude lower, resolution of the conflicting trends was even more problematic. Recognizing the need for cost‐effective expansion of fishery‐independent data in the region, we evaluated the performance of vertical longline surveys for sampling reef fish within a large artificial reef zone in the northern Gulf of Mexico. Specifically, we (1) determined species composition and the length frequency of red snapper (the dominant species captured) as a function of hook size and bait type within our survey area during 2010; (2) evaluated the effect of different soak times on catch for various hook types (a combination of hook size and bait type); and (3) utilized our results to test the effect of artificial reef type on red snapper CPUE and mean size. During March–November 2010, we conducted 532 vertical longline sets, capturing 1,217 red snapper that ranged from 184 to 827 mm FL. Mean FL of red snapper differed among hook sizes, with 3/0 and 8/0 hooks sampling smaller fish than 11/0 hooks. Soak time trials revealed a significant effect of soak time on CPUE, with peak catch rates observed at 5 min. As habitat area increased, the mean size and CPUE of red snapper increased. We conclude that our vertical longline is an effective gear for sampling red snapper, and we recommend protocols to maximize its utility and standardize its use.

Long-term catch and effort trends in Eastern Cape Angling Week competitions

Catches from Angling Week competitions between 1999 and 2010 were analysed to examine changes in catch and effort. Over the course of the study period there was a marked drop in the number of competing anglers and a significant reduction in the total number of fish caught (p = 0.026). There was also a significant (p < 0.01) shift in the areas fished by anglers, from predominantly sandy to rocky reef areas. A total of 5 786 fish, representing 46 different species and 24 families, were positively identified from catches recorded on 2 710 catch cards. Due to the inability of anglers to correctly distinguish between Mustelus mustelus and Triakis megalopterus and between Carcharhinus brachyurus and Carcharhinus obscurus, these species were recorded together into two taxa. The most commonly caught species were Argyrosomus japonicus (20.3%), Mustelus mustelus/Triakis megalopterus (13.0%) and Carcharias taurus (11.8%). Mean CPUE for all fish caught, teleosts and elasmobranchs, as well as the top four teleost and elasmobranch species, increased over the course of the study period, with the exception of Pachymetopon grande and C. brachyurus/C. obscurus, which decreased. Only C. brachyurus/C. obscurus exhibited a significant (p = 0.012) decreasing trend in mean annual weight. Many of the species (43.6%) caught during Angling Week competitions were smaller than published estimates of weight-at-50% maturity. These results, from a unique long-term dataset, provide important information towards the sustainable management of the Eastern Cape shore-fishery.

Catch and size selectivity of small-scale fishing gear for the smooth-hound shark Mustelus mustelus (Linnaeus, 1758) (Chondrichthyes: Triakidae) from the Aegean Turkish coast

Catch rate, CPUE, biomass ratios and size selectivity from traditional longline and trammel nets of Turkish coastal small-scale fisheries were investigated in order to describe the Smooth-hound shark (Mustelus mustelus) fishery. The SELECT method was used to estimate the selectivity parameters of a variety of models for the trammel nets inner panel of 150 and 170 mm mesh sizes. Catch composition and proportion of the species were significantly different in longline and trammel nets. While mean CPUE of longline was 119.2±14.3 kg/1000 hooks, these values for 150 and 170 mm trammel nets were 5.3±1.2 kg/1000 m of net and 12.7±3.9 kg/1000 m of net, respectively. Biomass ratios of the by catch to Smooth-hound catch were found to be 1:0.32 for 150 mm trammel net, 1:0.65 for longline and 1:0.73 for 170 mm trammel net. The estimated modal lengths and spreads were found to be 91.1 and 16.2 cm for 150 mm and 103.2 and 18.4 cm for 170 mm, respectively. The modal lengths of the species as well as the spread values increased with mesh size.

Freshwater Mussel (Unionidae: Bivalvia) Distributions and Densities in French Creek, Pennsylvania

The freshwater mussel (Unionidae: Bivalvia) communities of the French Creek watershed are nationally recognized for their importance to biodiversity. The goal of this research was to gather more information on the distribution and densi- ties of these species throughout the river. This study utilized two-phase sampling with timed searches to characterize mussel species richness in a large number of sites and to calculate catch-per-unit-effort values. The results of the timed search were used to select a subset of sites for quantitative mussel surveys to estimate density and abundance. Starting in New York, the main stem of French Creek was divided into 5.6-km lengths, and one site was randomly chosen within each of those lengths, favoring habitat (large riffl e/runs) for rare species and high species diversity. Snorkelers collected as many unionid individuals as possible, with a target search rate of 0.5 m 2 min -1 . Thirty-two main-stem sites were surveyed with timed searches. Mean species richness was 11.8 (SE = 0.94), and mean CPUE was 59.5 mussels per person-hour (SE = 9.32). Quantitative sampling was performed at ten sites using a double sampling design. Mean density estimates ranged from 0 to 27.98 m -2 . Abun- dance estimates range from 0 to 69,848 live mussels per site. For the main stem, we calculated regression models to estimate densities and abundances at qualitatively sampled sites based on the CPUE at quantitatively sampled sites. Extrapolation yields approximately 22 million mussels in the 2.04 million m 2 of large riffl e-run habitat in the main stem of French Creek.

Fishery and Aquaculture of Juvenile Mudskipper Pseudapocryptes elongatus (Cuvier, 1816) in the Coastal Zone of Mekong Delta, Vietnam

Mudskipper (Pseudapocryptes elongatus) has become a high value species (US$ 8 kg in June 2008) in the markets of Mekong Delta, Viet Nam. This leads to high pressure on its fishery and increasing interest on its aquaculture. An investigation was conducted on 40 juvenile fishermen and 72 mudskipper farmers in Soc Trang and Bac Lieu provinces of the Mekong Delta from May to December 2006. The P. elongatus juveniles fishing activity started in 2001 in the study areas. Collection of juveniles is conducted in spring tide periods from May to November. Juvenile collecting nets are set along the coast and interior river sites. The mesh size of net is 1 mm (body net) and 0.5 mm at cod end. Mean CPUE was 200,466 ind net in 6 months period. The juvenile catch is supplied to mudskipper farms, stocked at 16.2 ind m in semi-intensive and 95.7 ind m in intensive farms and fed local commercial feeds. Farming period is from May to December. Yields were 6.4 ton ha in intensive and 0.8 ton ha in semi-intensive farms. Production cost and net profit were US$ 8,696 ha and US$ 12,784 ha for intensive farms; and US$ 967 ha and US$ 1,039 ha for semi-intensive farms. Mudskipper aquaculture has potential for coastal aquaculture development and is an alternative to shrimp farming in the Mekong Delta. _________________________________________________ *Corresponding author. E-mail address: thminh@ctu.edu.vn 225 Asian Fisheries Science 23(2010):224-239

Associations between Watershed Characteristics and Angling Success for Sport Fishes in Mississippi Wadeable Streams

AbstractWe developed and evaluated multiple linear regression models to describe the associations between watershed land use and geomorphology and angling success (catch per unit effort [CPUE; fish/h]) for sport fishes in wadeable streams in Mississippi. The mean angler CPUE for all species combined, sunfishes Lepomis spp., and black bass Micropterus spp. was strongly and positively associated with the percentage of forest cover, stream density, total road density, and primary highway density. The mean angler CPUE of largemouth bass M. salmoides and longear sunfish L. megalotis was negatively associated with the percentage of agricultural land but positively associated with rural road density. The mean CPUE of spotted bass M. punctulatus was negatively associated with elevation and the number of road crossings in the watershed but positively associated with rural road density. Model validation procedures revealed that the prediction errors were relatively large, so that the ability to predict mean angler CPUE from individual streams was low for all models. However, the species group models were precise, explaining 83, 71, and 80%, respectively, of the variation in the mean CPUE for all species, sunfishes, and black bass from an independent data set. In contrast, the species‐specific models were relatively imprecise, explaining less than 33% of the variation in the mean CPUE in the independent data. We advocate a landscape‐level management perspective—in concert with more traditional assessments of water quality and biological integrity—to address the connection between sport fishing and conservation in wadeable streams in Mississippi.

Fish community structure in natural and engineered habitats in the Kansas River

AbstractWe investigated fish assemblage structure in engineered (rip‐rap) and natural habitats (log jams and mud banks) in the Kansas River USA to determine if natural structures had higher abundance and diversity of fishes at a local spatial scale. A total of 439 randomly selected sites were boat electrofished from May to August 2005 and 2006. Mean species diversity and richness were significantly higher in rip‐rap than log jams and mud banks. Mean relative abundance (CPUE; number of fish collected per hour electrofishing) of six of the 15 most common fishes (&gt;1% of total catch) were most abundant in rip‐rap, two were most abundant in log jams, and none in mud banks. Rip‐rap had the highest relative abundance of fluvial specialist and macrohabitat generalists, whereas mean CPUE of fluvial dependents was highest in log jams. Although a discriminant function analysis indicated that nine size classes (eight species) discriminated among three habitat types, the high misclassification rate (38%) suggested a high degree of fish assemblage overlap among the habitats. Although previous work has suggested that engineered structures (rip‐rap) and urbanization are linked to reduced biotic diversity or reduced growth of fish species, our results suggest that at a local scale rip‐rap may not have the same negative impacts on fish assemblages. Published in 2009 by John Wiley &amp; Sons, Ltd.

>Utilization of shallow subtidal bays associated with warm temperate rocky shores by the late-stage larvae of some inshore fish species, South Africa

>This work describes the utilization of shallow, subtidal bays, associated with rocky shores, by the late-stage larvae and early juveniles of some common inshore fishes. Larval and early juvenile fishes were collected in seven small bays (30–50 m wide) between Port Alfred (33°36’S, 26°53’E) and Hamburg (33°17’S, 27°29’E), using a modified, beach seine net (500 µm mesh). Four bays were sampled weekly during peak fish spawning (September–November 2004) to firstly assess whether larval fishes occur in these previously-unstudiedhabitats and secondly, to assess the extent of this utilization in terms of species occurrence, abundance and potential nursery function. An additional three replicate bays, situated >50 km away near Bira were used for comparison. In total, 14 fish families represented by 26 taxa were recorded but the catch was dominated by a small suite of common species. Bays were extensively utilized by Sparidae (>Diplodus capensis >and >Sarpa salpa>), and to a lesser extent by Clinidae (>Clinus superciliosus>), Mugilidae (>Liza >spp.) and Kyphosidae (>Neoscorpis lithophilus>). Mean CPUE of larvae was high and exceeded 900 individuals per seine haul. Larval abundance peaked at 4000 larvae per haul and at these times, was dominated only by the two sparid species. Abundance of sparid larvae exceeds that recorded for these species in surf zones, estuaries or the shallow nearshore habitatssampled to date in temperate South Africa by an order of magnitude. Larval abundance was significantly higher during new moon sampling throughout the study period, but was not significantly different between repeated samples collected per site on each fieldtrip. The length-frequency of larvae utilizing the bays was dominated by postflexion stages ranging 7–14 mm SL. Length-frequency distribution of >Diplodus, Sarpa, Clinus, Sparodon, Neoscorpis >was indicativeof grow-out and use of bays as interim nurseries. The nursery function of these bays is supported by gut analysis of a sub-sample of the dominant species, >Diplodus capensis, >which showed that these larvae were actively feeding in the area, predominantly on copepods. This work prompts further research on shallow habitats associated with rocky shores particularly the shelter and feeding role that these under-studied habitats are playing in the early life history of coastal fishes.

Relationship of precipitation, freshwater input, and sea level height with the abundance of the white shrimp ( Litopenaeus occidentalis; Street, 1871) off Buenaventura, eastern tropical Pacific

Penaeid shrimp fisheries are an important source of income for the fishing communities that live in estuarine zones around the world. Off Buenaventura, the habitat of the western white shrimp ( Litopenaeus occidentalis) is subject to high precipitation associated with the intertropical convergence zone, contributions from numerous short rivers descending from the Andes Mountains, and seasonal alternations in Trade Winds directions responsible for the upwelling in the Panama Bight. This work analyzes the relationship of precipitation, the San Juan River runoff, and sea level height with Litopenaeus occidentalis abundance in fishing areas between 1968 and 1989. The results indicate that precipitation is significantly correlated ( p < 0.01) with the catch per unit effort on a monthly scale with a lag of approximately 1 calendar year but the inclusion of the data in a transfer function model does not improve considerably the forecasting power of a simpler autoregressive moving average model of the catch per unit effort. On an annual scale, the catch per unit effort for white shrimp depends significantly [ r 2 = 0.36, p (corrected for autocorrelation) ≪ 0.01] on the precipitation that fell the previous December, whereas the residuals of this regression are significantly associated with variations of mean sea level between January and March (the upwelling season in the Panama Bight) of the current year at Buenaventura ( r 2 = 0.61, p (corrected for autocorrelation) ≪ 0.01). The inclusion of these two variables in a multiple linear regression model accounted for a substantial proportion of the total annual variance of the mean CPUE ( r 2 = 0.54), suggesting that freshwater contributions (lower salinities) and offshore transport during the main settlement period of postlarvae in the estuaries play a significant role in determining the strength of the cohorts recruited in the fishing areas. The industrial fishing yield decreased sharply after the 1982–1983 El Niño event. However, a high percentage of this change can be explained not by invoking El Niño effects but by a decreasing tendency of precipitation and offshore advection of early life stages between December and March, which took place on a multi-annual scale since the mid 1980s

Interactions between small cetaceans and the purse-seine fishery in western Portuguese waters

Marine mammal interactions with Portuguese purse-seine fisheries operating in four different ports (Figueira da Foz, Sesimbra, Setubal, Sines) were studied (July-October 2003). Observers accompanied commercial fishing vessels and monitored 48 fishing trips. An interview survey of skippers was also carried out (n = 36). Three species of marine mammals were observed in 31 sightings during the commercials trips but only the species Delphinus delphis and the category Delphinidae were observed to interact with fishing activities. Small cetaceans were observed to sink, gather or disperse school fishes and damage gear. Mean CPUE and fishing effort values did not change significantly in the presence of dolphins (H = 0.06 and H = 0, both p>0.05). Results from Figueira da Foz indicate that cetaceans are attracted to fishing grounds with a high abundance of their prey-species. Fishermen reported three by-catch events off Figueira da Foz. Compared with other fisheries, purse-seine fishing does not seem to be among the most damaging to marine mammals.

Shark fishing effort and catch of the ragged-tooth shark Carcharias taurus in the South African competitive shore-angling fishery

An integrated telephone and on-site questionnaire survey was used to estimate total shark fishing effort and specific catch of the ragged-tooth shark Carcharias taurus by coastal club-affiliated shore-anglers, primarily along the east coast of South Africa. Mean total shark fishing effort was estimated to be 37 820 fisher-days year−1 (95% CI = 28 281–47 359 fisher-days year−1) with a mean cpue of 0.073 C. taurus fisher−1 day−1 (95% CI = 0.068–0.078 fisher−1 day−1). Cpue for C. taurus varied significantly along the coast and ranged from a high of 0.260 fisher−1 day−1 in the Eastern Cape to zero fisher−1 day−1 on the West Coast. The total number of C. taurus caught annually by coastal club anglers was estimated at 1 764 fish year−1 (95% CI = 321–3 207 fish year−1). The majority (92.1%) of young-of-the-year sharks (<1.2m total length, TL) were recorded between East London and Jeffreys Bay, suggesting that this may be the primary nursery area for C. taurus. Post-release mortality ranged from 3.8% for young-of-the-year sharks to 18.5% for adult sharks (>2.4m TL). The majority (76.2%) of anglers interviewed stated that they now fished less for sharks since the banning of vehicles on beaches in December 2001. As a result of this ban, almost half (49.2%) of interviewed anglers stated that they now fished more for non-cartilaginous species.

Analogias ecológicas entre as assembléias de peixes de fundo dos estuários da Laguna dos Patos, Rio Grande do Sul, Brasil e York River, Virginia, EUA

The structure of estuarine fish assemblages at temperate latitudes in Patos Lagoon (32°05’S, 52°04’W), Rio Grande do Sul, Brazil and York River (37°17’N, 76°33’W), Virginia, USA was compared using mid and late 1970’s data from bottom collection to investigate whether geographically isolated fish assemblages have similar structure given similar latitudinal positions on the warm-temperate southwestern and northwestern Atlantic regions, respectively. Since estuarine species often exhibit an ontogenetic shift in habitat requirements or preferences we examined Capture per Unity of Effort by size class (CPUE-SC) and split species into “size taxa” (SET) for analysis. The use of CPUE-SC also allowed the abundance of a SET to be computed by summing the mean CPUE of each size class within that SET and use this information to follows SET’s temporal and or spatial abundance. A total of 65 and 63 species was collected during a year of bottom trawling in the Patos Lagoon and York River estuaries, respectively. In both localities the strongest modal size class was < 80 mm TL, and several abundant species were smaller than 100 mm TL. The size between 80 and 100 TL effectively separated several species into discrete SET’s in both systems. Those SET’s could have different ecological preferences, temporal and spatial distributions and so identified as different ecological taxa. In warm months, when predation by large fish is most likely, the abundance of fish between 80 and 100 mm TL in bottom trawl demersal fish assemblages was low in both systems. Only the sea catfishes, in Patos Lagoon, protected by strong dorsal and pectoral spines, and the Hogchoker, in the York River, protected by burrowing in the bottom substrate, peak in abundance at this size class. The seasonal pattern of estuarine use was similar between localities and did not differ from other warm-temperate estuarine fish assemblages.