Seine Catches Research Articles

Raspredelenie ulovov i razmernyj sostav navagi (Eleginus gracilis (Til.)) pri vedenii snyurrevodnogo promysla u zapadnogo poberezh'ya Kamchatki v 1995–2015 gg

Raspredelenie ulovov i razmernyj sostav navagi (Eleginus gracilis (Til.)) pri vedenii snyurrevodnogo promysla u zapadnogo poberezh'ya Kamchatki v 1995–2015 gg

Biomass and abundance biases in European standard gillnet sampling.

The European Standard EN 14757 recommends gillnet mesh sizes that range from 5 to 55mm (knot-to-knot) for the standard monitoring of fish assemblages and suggests adding gillnets with larger mesh sizes if necessary. Our research showed that the recommended range of mesh sizes did not provide a representative picture of fish sizes for larger species that commonly occur in continental Europe. We developed a novel, large mesh gillnet which consists of mesh sizes 70, 90, 110 and 135mm (knot to knot, 10m panels) and assessed its added value for monitoring purposes. From selectivity curves obtained by sampling with single mesh size gillnets (11 mesh sizes 6 – 55mm) and large mesh gillnets, we identified the threshold length of bream (Abramis brama) above which this widespread large species was underestimated by European standard gillnet catches. We tested the European Standard gillnet by comparing its size composition with that obtained during concurrent pelagic trawling and purse seining in a cyprinid-dominated reservoir and found that the European Standard underestimated fish larger than 292mm by 26 times. The inclusion of large mesh gillnets in the sampling design removed this underestimation. We analysed the length-age relationship of bream in the Římov Reservoir, and concluded that catches of bream larger than 292mm and older than five years were seriously underrepresented in European Standard gillnet catches. The Římov Reservoir is a typical cyprinid-dominated water body where the biomass of bream > 292mm formed 70% of the pelagic trawl and purse seine catch. The species-specific relationships between the large mesh gillnet catch and European Standard catch suggested that the presence of carp (Cyprinus carpio), European catfish (Silurus glanis), tench (Tinca tinca) or bream warrants the use of both gillnet types. We suggest extending the gillnet series in the European Standard to avoid misinterpretation of fish community biomass estimates.

Production of Anchovy and Mussel Pastes as Appetizer

Anchovy (Engraulis encrasicholus) is a species which mostly caught from Black sea by seine catch. This species represents the majority of the marine species consumed in Turkey. Mussel (Mytilus galloprovincialis) is a bivalve that has long been used as a marine food by boiling and stuffing with rice. It is harvested from Mediterranean, Aegean and Marmara sea and is mainly consumed in coastal towns. In this study, anchovy and mussel were used for raw materials. Subsequent to filleting the anchovy and extracting the meat of mussel, these two species were boiled in salty water and grinded. Ultimately, they were introduced separately to the mix of tomato paste, red pepper paste, swatted garlic, cumin, fenugreek powder, ground pepper, salt and olive oil. On account of its consistence, this developed product can be conserved in a paste tube as well as it can be bottled in a glass jar to preserve. The paste is suitable specially for use as appetizer in every repasts and can also be used as consistent intensifier and flavouring supplement during the cooking process. Aside from the production, the shelf life of the product was appointed by routine microbiological test methods (total aerobic mesophilic, psychrotrophic, coliform, Enterobactericeae, Micrococcus, Staphylococcus bacteria, yeast and moulds counts) and also the species of microorganisms found in pastes were identified. This is the first report about anchovy and mussel pastes describing microbiological flora.

Incidental spawning of some scombrids in Adriatic or not?

During routine monitoring of commercial purse seine catches in 2011, 87 fingerling specimens of scombrids were collected in the southern Adriatic Sea. Sequencing of mitochondrial control region locus inferred that specimens belonged to the Atlantic bluefin tuna, Thunnus thynnus (Linnaeus, 1758) (N=29), bullet tuna, Auxis rochei (Risso, 1810) (N=30) and little tunny, Euthynnus alletteratus, Rafinesque, 1810 (N=28). Due to previously published growth parameters, age of collected specimens was estimated to be approximately 30 days. In order to determine possible location of the spawning event coupled modelling system ROMS-ICHTHYOP was run. Realistic ROMS simulations were made to provide current and density fields for the ICHTHYOP model. ROMS model was forced with realistic surface air-sea fluxes calculated from fine resolution ALADIN model, river inflows, tides and external dynamics. ICHTHYOP was run in the backward mode for 30 days using published investigations on the studied species and its early stage dynamics, such as their growth and developmental stage thermal dependence, lethal temperatures, etc. Apart simulations with coupled modelling system, detailed analysis of prevailing meteorological and oceanographic conditions was made using all available data. Comparison to climatology of the area approved that 2011 had unusually prolonged warm and dry summer season. Occasional inflows of hot and dry air from the northern Africa additionally warm up Adriatic atmosphere. Under these conditions sea surface temperature was up to 2 standard deviations above normal. In the deeper layers, high temperature and salinity were recorded. According to performed simulations it seems that tuna species spawn within the commercial tuna cages (this is not the first evidence of natural spawning within commercial tuna farming facility in the Adriatic), while the other two species most probably opportunistically use positive environmental (abiotic and biotic) conditions and spawn in the same area.

Determination of Temporal Spawning Patterns and Hatching Time in Response to Temperature of Atlantic Bluefin Tuna (Thunnus thynnus) in the Western Mediterranean

This study analysed the temporal pattern of Atlantic bluefin tuna (ABFT) spawning in the Balearic spawning ground and examined its reproductive performance after years in captivity. Furthermore, ABFT hatching time at different on-site temperatures was determined for the first time. Spawning surveys were carried out in 4 spawning seasons (2009–2012) aboard tuna transport vessels. Three groups of spawners were monitored: a captive group transported to the spawning region and monitored throughout the four spawning seasons and two wild groups caught in 2009 and 2010 which were transferred to a monitoring transport cage immediately after being caught. Surface plankton samples were collected nightly, beginning immediately after the first purse seine catches were made and concluding after spawning was observed to have ended. All groups displayed the same spawning hours, restricted between 2:00–5:00 a.m. The captive group, as they got older, shifted towards the earliest hour, suggesting an age influence on reproductive time. The onset of spawning varied annually from the end of May to the beginning of June at temperatures around 19°C–20°C, ending by the second week of July. The peak of spawning was consistently around the summer solstice, June 15th–30th. The results showed the negative effect of unstable oceanographic conditions in the spawning process which might influence the annual reproductive success of ABFT. The influence of temperature on hatching time was higher than that observed in other tuna species, twice as fast at 26°C (23 h) as at 19.5°C (49 h). Overall, this study shows the strength of the internal mechanism in ABFT that controls spawning traits. Spawning in ABFT is cyclical and highly synchronised on diel and annual scales. We consider that the timing of spawning is rather influenced by day length and its adaptive significance is discussed.

Fisheries and biodiversity of the beach seine catch from the Eastern Harbor, Alexandria, Egypt

In the present study, the catch of beach seine operating in the Eastern Harbor of Alexandria (Egypt) during the fishing season of 2009 was investigated. Fishing is allowed all year except for some weeks in the winter. Catch efficiency was estimated to be 37.94kg/haul and catch rate was 25.29kg/h. The catch was classified into economic (60.24%) and non-economic (39.76%) species. The total number of species caught in the Eastern Harbor was 46 species (31 economic, 15 non-economic) belonging to 31 families (16 economic, 15 non-economic). The economic category of species was dominated by the immigrant sardine species Herklotsichthys punctatus while the non-economic category was dominated by Engraulis encrasicolus. Eight species were lessepsian. In terms of abundance, seven species were recorded during four seasons, seven species occurred in three seasons; ten species were found in two seasons while the rest occurred in one season only. Species compositions, size composition, the length-weight relationships as well as age composition for some dominant species were investigated. Fishing in sheltered places or nursery grounds with small meshed nets (0.5cm) causes drastic danger to the fish populations of the Eastern Harbor.

Nearshore Fish Assemblages of the Northeastern Chukchi Sea, Alaska

The Arctic ecosystem is changing rapidly, yet information on nearshore fish assemblages for the northeastern Chukchi Sea is extremely limited. To address this information gap, we sampled nearshore fish assemblages with a beach seine and a small bottom trawl at six stations in the northeastern Chukchi Sea in August 2007, 2008, and 2009, and in September 2009. Catch and species composition differed by gear type and between sample periods, including the two in 2009. A total of 16 039 fish representing 18 species were captured in 24 beach seine hauls, and 3108 fish representing 24 species were captured in 48 trawl tows. Beach seine catch was dominated by capelin (83%), and trawl catch was dominated by Arctic cod (56%). Species that were good discriminators between gear types were capelin (seine) and slender eelblenny (trawl), and unidentified small sculpins were the most common taxa caught with both gear types. Capelin and Arctic cod captured by either gear type were mostly juveniles (judging by size). Variability among sampling periods in catch and species composition within gear types can likely be attributed to annual variations in environmental conditions, including differences in water temperature (range: 2˚–9˚C). The shallow nearshore environment of the northeastern Chukchi Sea provides important habitat for many fish species and is extremely vulnerable to disturbance. Loss of sea ice from global warming may open up formerly inaccessible areas to oil and gas exploration, vessel traffic, and commercial fishing. Thus, long-term monitoring of nearshore fish assemblages in the Alaskan Arctic is necessary for managers to make informed decisions in this fragile environment.

Sampling Gear Efficiency and Selectivity for Juvenile Ladyfish Elops Saurus in Florida Waters (USA)

At the foundation of managing wildlife is collecting accurate field data with appropriate sampling gears and methods under a strict experimental design and standardized protocols. To elucidate, monitor, and predict wildlife patterns in space and time requires the selection of specific sampling gears for the community or species of interest, especially for species that display spatial and temporal variability in distribution and abundance. Among the most challenging types of wildlife to examine in the field are marine fisheries resources given their expansive range, spatial and temporal distribution, and specific early life-history characteristics (e.g., habitat, environmental conditions, and recruitment patterns). Numerous studies have investigated the catch efficiency for various sampling gears and techniques; however, no information has ever been reported for ladyfish (Elops saurus), an economically valuable species in the southeastern United States and other world-wide regions. Given the importance of collecting ladyfish early life-history information, the purpose of this investigation was to evaluate, for the first time, the efficiency and selectivity of various field-sampling gears used in Florida waters to collect juvenile ladyfish. The specific objectives were to examine the sampling gear efficiency and selectivity on juvenile ladyfish relative abundance and length-frequency distribution among different water bodies. This investigation found that juvenile ladyfish abundance, size, and length frequency distribution significantly varied by sampling gear. In addition, the findings revealed that the most efficient gear for sampling juvenile ladyfish smaller than 100 mm SL were seines with an offshore deployment method. Despite detecting length frequency differences among sampling gears, no clear pattern was evident among estuaries. In general, seine catch efficiency decreased and gillnet efficiency increased with ladyfish size. To alleviate gear or sampling bias, results demonstrated that researchers need to use a variety of sampling gears to sample ladyfish.

Seasonality and Spatial Variation in Nekton Assemblages of the Lower Apalachicola River

The results of statistical analyses conducted on monthly trawl and seine data collected from a multiyear fisheries-independent monitoring program, between July 2006 and March 2009 on the lower Apalachicola River, FL were used to determine which regions of the river, and what time of year should be further studied to determine if and how freshwater flow alterations affect the nekton. Differences in nekton community structure were clear between each of the 3 predefined habitat regions for shoreline seine catches. Deepwater trawled habitats showed a distinct difference between the upper river channel and both distributary regions, and less pronounced differences between the two distributary regions. The strongest pattern in seasonality of nekton communities coincides with seasonal fluctuations in recruitment of juveniles into the estuary and the periods of greatest salinity differences in the marshgrass-dominated lower distributary region for shoreline and deepwater habitats. Seasonal variations in community structure were evident and mostly likely dominated by recruitment, whereas the response of organisms to fluctuations in salinity may be dictated by their relative position within the lower reaches of the Apalachicola River system. Our results suggest that future studies of the effects of changes in flow on nekton assemblages in the lower Apalachicola River would best be performed during the dry season in the upper and lower portions of the distributary region.

Global spatio-temporal patterns in tropical tuna purse seine fisheries on drifting fish aggregating devices (DFADs): Taking a historical perspective to inform current challenges

This study provides a historical overview of the use of drifting fish aggregating devices (DFADs) in purse seine fisheries since the early 1990s, using global tuna fisheries datasets from the four tuna Regional Fisheries Management Organizations (RFMOs). Tropical tuna purse seine fisheries typically target large yellowfin (Thunnus albacares) and bigeye (Thunnus obesus) tunas on free-swimming schools and skipjack (Katsuwonus pelamis )a nd juveniles of yellowfin and bigeye associated with drifting objects. DFADs have enabled global skipjack catches to markedly increase, and have also introduced major scientific issues for all tuna-RFMOs. In particular, they have strongly modified the fishing strategies of purse seiners that fish on a combination of free-swimming and DFAD-associated schools. Consequently, the cumulated search time traditionally used to quantify nominal fishing effort to assess the status of tuna stocks is inconsistent and cannot be used to derive time series of abundance indices from catch-per-unit of-effort (CPUE). In addition, the lack of information available on the construction, deployment, and use of DFADs has prevented effective monitoring of the fishing pressure over the last two decades exerted by purse seine fleets using this fishing mode. Juveniles of tropical tunas represent a substantial proportion of purse seine catch on DFADs in the three oceans, which has raised particular concern for some bigeye stocks that have been subject to overfishing in the past. Catches of juvenile tunas by DFAD fishing may also result in a decrease in recruitment for fisheries that target adult tunas such as longliners. In addition, some demographic parameters of tunas and other species associated with DFADs may be affected by the resultant habitat modification arising from the widespread deployment of DFADs. Evidence in the literature and provided by the ratio-estimator method suggest that fishing DFAD-associated schools may result in about 100 000 t of bycatch and discards annually. In addition, there is further potential for ghost fishing related mortality of sensitive species such as marine turtles and pelagic sharks. In this context and following a precautionary approach, we finally discuss the increasing need for all tuna-RFMOs to reduce, or at least monitor and control, the use of DFADs to mitigate their adverse effects not only on yellowfin and bigeye stocks but also on open-ocean ecosystems.

Fish biomass estimates along estuaries: A comparison of vertical acoustic sampling at fixed stations and purse seine catches

Two techniques, the conventional purse seine method and a novel method using vertical hydroacoustic surveys at fixed positions, were applied simultaneously in the Gambia River estuary to sample a fish population. Environmental parameters were measured simultaneously. Four surveys were performed during different hydrological seasons to reflect the main sources of variation in the environmental conditions of the estuary. A total of 153 samples resulted from these surveys. To identify the environmental conditions in which the two methods yield similar pictures of the fish population, a regression tree was constructed in which the dependent variable was the difference between the standardised values of the catches from the purse seine and the estimated biomass from the acoustic samples. A highly significant correlation was found between the two approaches using a set of data (128 samples) that excluded the samples with specific environmental conditions (downstream samples with high transparency, and upstream ones with high transparency, high depth and high temperature). We conclude that, except under these specific environmental conditions, vertical hydroacoustic samples recorded at a fixed station can serve as a proxy of the catches from a purse seine and can allow the monitoring of fish biomass in estuaries without damaging the environment.

The size selectivity of the main body of a sampling pelagic pair trawl in freshwater reservoirs during the night

The aim of this study was to test the selectivity of a trawl main body, especially for small fish, during night sampling. The tested trawl had a mesh size of 80/40/20mm in the main body, a mouth opening of approximately 100m2, and a length of 48m and was originally designed for sampling vendace, Coregonus albula L. Trawl selectivity was determined by comparing the catch using this gear with that from a purse seine net (mesh size 6–10mm, length 120m, height 12m) at the same sites and time. The size distributions of the total catch and densities of three dominant species (common bream, Abramis brama (L.), roach, Rutilus rutilus (L.) and bleak, Alburnus alburnus (L.)) were compared between the two types of gear. Densities of these species were divided into size groups before comparison: (i) small fish (60–120mm, standard length SL); (ii) middle-sized fish (125–180mm SL); and (iii) large fish (>180mm SL), which included only roach and bream. Significant differences in the fish density between the trawl and purse seine nets were found. Generally, the densities in all size categories of bleak and small roach were underestimated in trawl catches, whereas the densities of middle- and large-sized bream were underestimated in the purse seine catch. We conclude that both types of gear are size selective – small fish escaped through the mesh of the trawl main body, whereas larger bream were able to escape from the purse seine before closing. The trawl with the given mesh sizes is recommended for quantitative sampling only of fish larger than 180mm (SL) under low light-intensity conditions.

가공공장에서 수행한 한국 다랑어 선망 어획물 종조성에 대한 예비 연구

A preliminary study on species composition of a Korean purse seine catch landed at cannery was conducted in April 2011. In the cannery, all tuna catch are sliding through a sorting grid panel that filters and drops fish in the buckets by size class (above 9kg, 3.4-9kg, 1.8-3.4kg, 1.4-1.8kg and below 1.4kg). In cannery processing, species sorting was made for skipjack tuna and yellowfin tuna only from catches greater than 3.4kg during filtering but not for bigeye tuna because of difficulties in species identification between bigeye tuna and yellowfin tuna under frozen state. As no species identification was carried out for catch groups less than 3.4kg in the cannery process, this study focused on sorting out skipjack tuna and yellowfin tuna from these groups and then identifying bigeye tuna from all size groups of yellowfin tuna. Using the mixture rate of species obtained from the samples taken, species composition of the landed catch was estimated. As results, cannery research showed 95% for skipjack tuna, 3% for yellowfin tuna and 2% for bigeye tuna in species composition, while vessel logbook data represented 96%, 3% and 1% for skipjack tuna, yellowfin tuna and bigeye tuna, respectively. The proportion of bigeye tuna identified in the cannery was slightly higher than shown in logbook data by 1%.

Exploitation of small indigenous fish species using shore seines in three reservoirs of Sri Lanka

The fish resources in reservoirs of Sri Lanka are not efficiently harvested due to various reasons such as gear and mesh restrictions and consumer preference. However, there is a potential for augmenting reservoir fisheries production by exploiting under-exploited and unexploited fish resources in reservoirs. In the present study, an attempt was made to investigate whether shore seining could be effectively used for differential exploitation of small indigenous fish species in three Sri Lankan reservoirs. It was found that shore seining was not effective for catching all species present in reservoirs. The index of relative importance determined for fish species indicated that apart from the differences between reservoirs, their relative importance in the shore seine catches was influenced by the water level of the reservoir. It is evident from the present study that in order to establish a fishery for this under-exploited species, shore seining is the appropriate fishing strategy. However, such a fishery is needed to be strictly managed for preventing indiscriminate exploitation of exotic cichlids in Sri Lankan reservoirs, which form productive fisheries. DOI: 10.4038/sljas.v13i0.2205 Sri Lanka J. Aquat. Sci. 13 (2008): 39-50

Fish biomass and species composition in the Malta Reservoir, Poland

In the Malta Reservoir a total of 16 fish species belonging to six families were recorded in 2008. In the Nordic multi-mesh gillnets 4528 fish belonging to 11 species, with the total weight of 149.5 kg, were caught. The total beach seine catch was 34348.9 kg, which in terms of the reservoir area of 64 ha amounted to biomass density 536.7 kg·ha. Of 11 species caught with the beach seine roach (Rutilus rutilus) was the most abundant species (485031 fish, 7578 individuals·ha) with the highest share in biomass (24283.4 kg, 70.7%). The average electric catch at two sampling sites in the Cybina River running in the reservoir bowl was 105 kg (which gave estimate of 2.6 ton in all), with a marked dominance of the roach, which constituted 65.4% of fish catch in weight and 93% in numbers. Taking under consideration the results of electrofishing the estimated fish density in the Malta Reservoir in 2008 could reach as much as 577.7 kg·ha. The proportion of predatory fish in the fish assemblage biomass was 20.1%.

Fish Diversity and Abundance in Relation to Interannual and Lake‐Specific Variation in Abiotic Characteristics of Floodplain Lakes of the Lower Kaskaskia River, Illinois

AbstractThe importance of floodplain lakes to tropical river systems is well established, but little is known about the function of these habitats in temperate river systems. We examined fish diversity, abundance, and reproduction within six oxbow lakes of the Kaskaskia River, Illinois, over 5 years and their relationship to 11 abiotic environmental variables. The lakes were hydrologically dynamic within and among years, varying in the time connected with the main stem (0‐22 weeks/year) and the frequency of low (<0.3‐m) water (0‐23 weeks/year). Differences were found both among years and lakes. All measured limnological variables (dissolved oxygen, Secchi disk depth, conductivity, and temperature) varied temporally, but only conductivity and Secchi disk depth varied among lakes. Fish species differed among lakes and between adjacent lotic habitats, and species‐specific abundance varied among years, seasons, and lakes. This variation was related to several environmental variables. Diversity was positively related to the distance between the oxbow lake and the river but not to any variables that had interannual variation. Seine catch per unit effort (CPUE) was negatively related to mean water level and Secchi disk depth. Total electrofishing CPUE was not related to any variables; however, that of bluegills Lepomis macrochirus was positively related to maximum depth and that of warmouths L. gulosus was positively related to vegetated area. Across all lakes, evidence of reproduction was found for five species and was negatively related to the mean water level and frequency of low water and positively related to flood periodicity. The oxbow lakes have the potential to contribute to the fish community of the main river by providing spawning and nursery habitat for several fish species as well as helping maintain several less abundant main‐stem species. However, when considering management options to maintain or restore these ecosystem functions, interannual variation in environmental variables, particularly those related to flood periodicity, should be considered.

Comparison of mesenteric and tissue fat content in relation to sexual cycle of the sardine,Sardina pilchardus(Walb., 1792), in the eastern Middle Adriatic fishery grounds (Croatia)

The study objective was to analyse Sardina pilchardus (Walb., 1792) for mesenteric fat, which is easier to evaluate than the muscle lipid, for comparisons thereof with the sexual cycle and condition of the examined specimens. Fat reserves, moisture and the sexual cycle of sardines were studied from monthly random samples of purse seine catches from March 2004 to February 2005. A total of 1209 specimens were collected (668 males; 541 females). Total length and mass ranged from 13.0 to 19.0 cm and from 16.7 to 51.5 g, respectively. Lipid analyses in muscle tissues were done using the Soxhlet method. An inverse relation between fat content and the sexual cycle was established. Greatest fat quantities were observed in August (72%) during the gonadal resting phase; lowest values were noted in winter, and in spring during the spawning period peak. Moisture content and sexual cycle were positively correlated (r = 0.7913). Total lipids in sardine tissues were higher in females than in males; however, the moisture content was higher in males than in females.

Trends in trawl and purse seine catch rates in the north-eastern Mediterranean

Data on fishing effort expressed in vessel days at sea and corresponding landing/day for a large number of species have been collected by the Institute of Marine Biological Resources (IMBR) since the second half of 1995. Data were collected over a grid of 21 stations throughout the Greek seas. In the present study we analyzed the monthly days at sea as well as catch per day for trawlers and purse seiners from 1996 to 2000, by general linear models and trend analysis. The following vessel size groups per gear were considered: (a) trawlers smaller and larger than 20m; (b) purse-seiners smaller and larger than 15m. Collected data were also aggregated for five fishing sub-areas: the North Aegean, the Central Aegean, the South Aegean, Cretan waters and the Ionian Sea. Trend analysis of landing/day time series indicated that demersal and pelagic resources are declining in the main fishing grounds. Declining landing/day trends are regarded as indicators of overfishing, especially in the light of the fact that high catch rates are maintained by fishing in ‘hot spots’. The results of the present analysis provide, for the first time, important information on the sustainability of the fisheries in the north-eastern Mediterranean, an area characterized by a complete lack of accurate long-term data on effort and catch per effort

Short-term Effects of a Partial Drawdown on Fish Condition in a Eutrophic Reservoir

Prescribed or natural drawdowns occur frequently in reservoirs but their effects on fish populations have been barely studied. As a consequence of a severe drought and the need to optimize water quality, a partial drawdown was prescribed in autumn 2005 to a eutrophic reservoir that provides water supply to a large metropolitan area (Barcelona, Spain). In order to avoid a potential massive fish kill given the reduced oxygen availability and high fish abundance, preventive purse seine fisheries were performed to reduce the fish stock. The fisheries had little effect on the fish assemblage because final population size structure and species composition did not change significantly. The species composition of the purse seine catches varied significantly during the drawdown with higher proportion of bleak (Alburnus alburnus) in pelagic water during the days of worst water quality, confirming that bleak is more tolerant than roach (Rutilus rutilus) to poor water quality and a potential good indicator of water pollution. The weight–length relationship (i.e. condition) of roach and bleak also varied significantly during the drawdown following the same tendency in both species, losing and recovering their weight (4.99% in roach and 5.96% in bleak) in only 16 days. The close relationship found between water quality and fish condition demonstrates that fish condition can be a good metric of the well being of fish, even for extreme short-term changes.

Climatic oscillations and tuna catch rates in the Indian Ocean: a wavelet approach to time series analysis

AbstractWe analysed the influence of climatic oscillations [based on the Indian Oscillation Index (IOI)] on monthly catch rates of two tropical tuna species in the equatorial Indian Ocean. We carried out wavelet analysis, an efficient method of time series analysis to study non‐stationary data. Catch per unit of effort (CPUE) of bigeye tuna was computed from Japanese longline statistics from 1955 to 2002 in the equatorial Indian Ocean and CPUE of yellowfin tuna was derived from industrial purse seine statistics from 1984 to 2003 in the Western Indian Ocean. Wavelet analyses allowed us to quantify both the pattern of variability in the time series and non‐stationary associations between tuna and climatic signals. Phase analyses were carried out to investigate dependency between the two signals. We reported strong associations between tuna and climate series for the 4‐ and 5‐yr periodic modes, i.e. the periodic band of the El Niño Southern Oscillation signal propagation in the Indian Ocean. These associations were non‐stationary, evidenced from 1970 to 1990 for bigeye, and from 1984 to 1991 and then from 1993 to 2001 for yellowfin. Warm episodes (low negative IOI values) matched increases of longline catch rates of bigeye during the 1970–1990 time frame, whereas the strong 1997–1998 warm event matched a decrease of purse seine catch rates of yellowfin. We discussed these results in terms of changes in catchability for purse seine and longline.