Commercial Catch Statistics Research Articles

Quantifying the unreported and unaccounted domestic and foreign commercial catch of sharks and rays in Western Australia.

Reliable catch information is scarce for most sharks and rays worldwide, with almost half of the stocks considered to be Data Deficient due to limited species-specific catch statistics. Western Australia (WA) hosts a diverse number of shark and ray species, some of which are considered to be threatened with extinction at a global level. Commercial catch statistics only account for shark and ray landings. The present study used the best available information to reconstruct unaccounted and unreported catches for 47 shark and ray taxa to better understand the impact of fishing. For some species, there was good agreement between reconstructed catches and reported landings, but overall reconstructed catches were 57% higher than those derived from official statistics alone, underestimating the actual extraction level for many species. The reconstructed catch time series provide the basis for the assessment of all species of sharks and rays captured in WA, including protected species that interact with commercial and recreational fisheries.

Some Targeted Reference Points for Thin Lip Grey Mullet Liza ramada Management in Bardawil Lagoon, North Sinai, Egypt

The evaluation and management of fisheries resources require knowledge of spatial and temporal changes in the habitat-associations of fishes as well as studying the biology and dynamics of commercial fishes of that fishery. The thin lip mullet, L. ramada is one of the most important and high valued species in Bardawil lagoon, Egypt. Long term commercial catch statistics show a significant decrease in the commercial landings of grey mullet in Bardawil lagoon since 1995. By learning more about this species and protecting the habitat upon which it depends, we can ensure that this important valuable fish remains abundant. Age was determined based on scale’s readings of fish collected in May 2017 to December 2017 and in May 2018 to October 2018. Growth parameters, mortality rates, exploitation level as well as the critical lengths and ages were estimated. Based on yield per recruit analysis, the mullet fishery in Bardawil lagoon was found to be heavily exploited. The study suggested some applicable reference points for sustaining and optimizing the thin lip grey mullet yield in Bardawil lagoon.

Long-term occurrence of Atlantic bluefin tuna Thunnus thynnus in the North Sea: contributions of non-fishery data to population studies

The sudden disappearance of Atlantic bluefin tuna in northern Europe in the 1960’s, after its frequent occurrence in the preceding period, has often been discussed in the scientific literature. Remarkably enough, the question whether the figures from the beginning of the 20th century have always been at the same high level in earlier periods, has so far only been poorly investigated. The answer to this question is crucial to define realistic targets for conservation measures aiming at the return of bluefin tuna to this feeding area. Taking account of texts from 16th to 19th century authored by naturalists and zoologists, and scientific papers by fishery biologists in the early 20th century, it is concluded that tuna has frequently been present over the last centuries but their abundance has not been consistently high. This conclusion is supported by national newspaper databases which help to learn more about age group distribution, fishery, and local differences in consumer acceptance with regard to tuna in the 1910’s. These sources revealed two new ecological insights to bluefin tuna ecology in the region. First, the documents showed an earlier phenology than can be seen from most of the 20th century commercial catch statistics, with occasional sightings and strandings during March-June. Second, schools of bluefin tuna appeared in the Rhine-Scheldt estuary in the first decades of the 20th century.

DINAMICA POBLACIONAL DEL CHIVO MAPALE Cathorops spixii EN LA CIENAGA GRANDE DE SANTA MARTA Y COMPLEJO PAJARALES, CARIBE COLOMBIANO

During 1994, the catfish "chivo mapalé" (Cathorops spixii) was the second most abundant fishing resource in the "Ciénaga Grande de Santa Marta" and the "Complejo de Pajarales", the main lacustrine-estuarine system of Colombia. Using commercial catch statistics and fishing explorations, the population parameters were determined reproductive cycle, growth, mortality, yield and biomass per recruit. Mature individuals were present all year around with peaks of ripeness and spawning from June to August during periods of little rain and dry, respectively. The mean maturity size was estimated at 23 cm. The growth parameters of the Von Bertalanffy function were: Loo = 32.5 cm and K = 0.38 year1, with a growth performance index of 2.6. Total (Z), natural (M) and fishing (F) mortality rates were estimated as 2.83, 0.96 and 1.87 year1, respectively. The exploitation rate E = 0.66 indicates that the resource is overfished. Therefore it is recomended a fishery regulation by decreasing the mortality rate to F = 1.0 year1 and increasing the cath mean size to 23 cm.

The use of spearfishing competition data in fisheries management: evidence for a hidden near collapse of a coastal fish community of Galicia (NE Atlantic Ocean)

AbstractThe use of commercial catch statistics to estimate overfishing consequences has been criticised, but alternative long‐term data sets are rare. Long time‐series data sets from recreational fisheries competitions have been used to infer trends in coastal fish communities. Here an historic archive (1953–2007) of recreational spear fisheries in Galicia (NW Spain) was employed to estimate long‐term changes in coastal ecosystems. Using generalised additive regression models, decreases in the abundances of coastal rocky reef fishes of up to 76% over the last 50 years were found. In the same period, the mean body weight also decreased by 76%. In addition, relative catch frequency has decreased for the most valuable commercial species. Overfishing, amongst other human impacts, has brought these ecosystems so close to collapse that it is urgent to implement measures to ensure their recovery.

Calming down the seas: the near collapse of an Atlantic coastal fishery

AbstractFor years now the estimates of the consequences of overfishing for marine ecosystems have differed greatly within the scientific community^1^. The use of commercial catch statistics to estimate tendencies has been much criticised^2^, but alternative information sources with long time series are rare. Here we employ the historic archive (1953-2007) of the recreational spearfishery in Galicia (NW Spain), which does not have the problems common to other fishery registers, to estimate long-term changes in coastal ecosystems. Using generalized additive regression models (GAM) we estimated decreases of around 83% in the abundances of coastal fish over the last 50 years. In the same period the average body size decreased by 36%. In addition, the relative catch frequency has decreased for the most valuable commercial species. Commercial overfishing has brought these ecosystems so close to the brink of collapse that it is necessary to implement measures that ensure their recovery.

Assessing shifts in fish assemblages of German large lakes by literature data and commercial catch statistics

To assess the ecological integrity of lakes according to the European Water Framework Directive, the present status of fish assemblages has to be compared to a type-specific reference status. Monitoring fish assemblages by standardized fish sampling surveys as recommended for smaller lakes can be performed in large lakes only by an extraordinarily high effort and with severe doubts in terms of representative sampling. As an alternative, we present the evaluation of fisheries data from historic and present catch statistics and literature for the 26 lakes > 10 km 2 surface area in Germany. Documented species-specific fish catches were classified into four abundance classes for both the historic and the present situations. Cluster analyses of the historic and the present fish abundance matrices revealed that fish assemblages mainly differed between ecoregions and watersheds. Local species extinctions and abundance declines were frequent in some lakes and most often occurred in the fish families Core-gonidae and Salmonidae. However, in almost 60 % of all species present, no changes in abundance classes were found. Lake-specific changes in fish assemblage composition were correlated to present trophic situation, natural shore structure and human use intensity, but the correlations differed between ecoregions and watersheds. Shifts in relative species abundances were only partially correlated to species turnover rates, based on presence/absence lists. Accordingly, human impacts on lakes predominantly modified the relative species abundances rather than resulted in massive species extinctions or a dominant establishment of invaders. Extensive literature data may be a valuable source of information to fulfil the demands of the WFD for a fish-based assessment of the ecological state of large lakes for which comprehensive data sets exist and thereby offer a cost-effective alternative to effort-intensive test fishing.

Return of twaite shad Alosa fallax (Lacépède, 1803) to the Southern Baltic Sea and the transitional area between the Baltic and North Seas

The status of twaite shad was investigated within the Southern Baltic Sea (ICES subdivision 22–27) and transitional area between the Baltic and North Seas (division IIIa). The following sources of data were analysed: (i) commercial catch statistics and relevant publications, (ii) records from ichthyological museum collections, (iii) records from recent commercial and recreational fisheries, (iv) research fisheries with trawls. A total of 476 records of twaite shad including more than 16 million individuals were obtained for the time between the years 1836 and 2005. About 72.9% of all records originated from commercial catch statistics and publications, whereas 18.9% were received from ichthyological collections. Research fisheries provided 6.3%, and 1.9% of the records were obtained from recent commercial and recreational fisheries. Most records of twaite shad were estimated for subdivisions 24 (45.2%) and 26 (35.5%). From 1836 to 1959, 29.6% of the records date from the period until 1899. 70.4% of the records of twaite shad originate from the twentieth century until 1959. The mean annual catch of twaite shad between 1891 and 1959 amounted to 86,674 kg within subdivisions 24–26 of the Southern Baltic Sea. Catch data show an approximately 20-year-cyclicity of maximum yields and minimum catches, respectively. The maximum annual yield of twaite shad in subdivisions 24–26 (474,700 kg) was registered in 1940, the minimum annual yield was estimated in 1958 (10 kg). In the 1950s, the annual catches of twaite shad declined sharply. Until 1960 twaite shad catches and records originated mainly from the Pommeranian Bay/Pommeranian Coast and adjacent waters including the Szczecin Lagoon (subdivision 24), the Bay of Gdansk, Vistula Lagoon and Vistula Spit (subdivision 26) and from the Curonian Lagoon and Curonian Spit (subdivision 26). The highest catches of twaite shad originated from the area of Curonian Lagoon/Curonian Spit from 1941 to 1960. Seasonal catches of twaite shad showed maximum values from May to July. From 1960 to 1989, only four records of A. fallax were registered in the Southern Baltic Sea which originated from German coastal waters in subdivisions 22 and 24. A total of 107 records of twaite shad was obtained in subdivisions 20–27 from 1990 to 2005. Most of these recent records originate from a twaite-shad stock in subdivisions 24, 25 and 26. There are indications which suggest a separate stock of twaite shad in subdivisions 20 and 21. Disappearance and recovery of twaite shad stocks were probably caused by the following factors: construction of barriers in rivers with spawning sites of twaite shad; habitat destruction in those rivers as consequence of gravel extraction and reengineering scheme to improve navigation and for flood defence purposes, water pollution in the lagoons of the Southern Baltic and in their tributaries, commercial fishery in the Southern Baltic and climatic variation in the Baltic Sea basin south of the latitude of 60° N.

Use of fishery‐dependent data for the evaluation of depensation: Case study involving the predation of rock lobster (Jasus edwardsii) by octopus (Octopus maorum)

The relationship between the level of octopus (Octopus maorum) predation and the daily‐average number of lobsters (Jasus edwardsii) per pot was investigated using commercial catch statistics. Octopus predation was found to be inversely correlated with lobster catches, such that, lobsters experienced reduced survival when their daily‐average density in a pot was lower. The reduction in survival at lower densities provides evidence for a depen‐satory mechanism underlying the predator‐prey interaction between pot‐caught octopus and lobster. The effect of lobster density on the feeding response of octopus is unknown so this study could not determine whether depensation was brought about by either predator saturation or predator avoidance tactics used by lobsters. The use of commercial catch statistics to investigate this depensatory effect has disadvantages because the lobster mortality estimates can be biased by the non‐reporting of undersized lobsters caught inside pots, under‐reporting of lobsters killed by octopus, the inability to identify unsuccessful predation attempts made by octopus, and the ability of some lobsters to escape from pots. All the sources of bias would tend to make it difficult to conclusively determine both the absolute proportion of lobsters killed by octopus and the true scale of the depensatory mortality, as the scale of the mortality may be greater than the commercial data suggest. However, the bias will not necessarily reduce our ability to detect the depensatory effect if, as seems likely, the sources of bias are relatively constant across the range of daily‐average catches. Depensation in crustacean stocks affected by pot‐related octopus predation has been rarely studied, and, because depleted stocks lead to fewer lobsters being caught per pot, such depensatory mortality has implications for the population dynamics and management of crustacean stocks.

Using commercial catch statistics to detect habitat bottlenecks in large lowland rivers

AbstractThirty‐seven years of fisheries records covering a fishing area of 6231 ha in the lower Havel River, Germany, have been analysed to address two issues: (1) detection of the effects of habitat bottlenecks caused by extreme floods and droughts on adult fish assemblage; and (2) evaluating the appropriateness of commercial fisheries statistics in testing the habitat bottleneck concept. Time series analyses of the data were first tested for autocorrelations and then classified using the CHAID (Chi‐squared Automatic Interaction Detector) and C&RT (Classification and Regression Trees) algorithms. The significant environmental predictors revealed by these segmentation procedures were used in cross‐correlations with various time series of fisheries yields. No single hydraulic flood parameter was significantly correlated with fisheries yield but two drought parameters were. The strongest predictor of native fish species was the minimum discharge during the spawning season (March to June). Although total fisheries yield typically increased in years with low flows, probably because of higher catch efficiencies, the yields of pike and pikeperch significantly decreased in the following two years. By comparison, significantly higher catches of pike, perch, asp, burbot, and ide were recorded in the three years following periods of sustained higher base flows. Our findings suggest that habitat bottleneck effects on fish assemblages have an important role in influencing fish community structure and do require further study. Information on habitat bottlenecks will contribute to the setting of ecological flow requirements and sustainable fisheries in large rivers systems. Copyright © 2005 John Wiley & Sons, Ltd.

Comparing survey and assessment data: Consequences for stock evaluation of Northeast Arctic Greenland halibut

Based on VPA-estimates of abundance, survey data and commercial catch statistics of Northeast Arctic Greenland halibut (Reinhardtius hippoglossoides Walbaum), the paper describes trends by year-class and age in the distribution of Greenland halibut between surveyed and not-surveyed areas. Changes in the distribution of I-group around 1990 to areas beyond the Svalbard surveys has previously been described and related to temperature changes in the Spitsbergen Current. This paper shows that this displaced distribution of the 1989-94 year-classes persisted up to age 7. The results indicate that the displacement was an extraordinary situation and other similar distribution shifts have not occurred during the last 30 years or more. Further, the shift co-occurred with extreme levels of the 137 year long time series of the index of the North-Atlantic Oscillation (NAO). The results are discussed in relation to stock management and climate change.

A survey-based assessment of the Northeast Arctic cod stock

Acoustic and bottom trawl surveys of the Northeast Arctic cod stock provide fishery independent estimates of abundance and population characteristics. Given the recent uncertainties in the catch based assessment of the stock, survey based abundance estimates of ages 5+ cod and spawning stock biomass, generated by calibrating survey indices with converged estimates from a virtual population analysis (VPA), were compared with the estimates from the annual assessments. The results indicate that the survey-based estimates were more accurate than the estimates from the annual assessments. Since the VPA abundance estimates for younger cod tend to be inaccurate, the amount of information contained in the surveys was tested indirectly by determining how well estimates based on previous survey indices could predict the following year's survey value. A time-series model of ages 3+ cod and haddock survey indices predicted the subsequent value of the cod survey index fairly accurately. It is concluded that it is likely that these fishery independent surveys are providing a more accurate assessment of the current size of the cod stock than the assessment based on combining the survey data with commercial catch statistics.

Fish do not avoid survey vessels.

The precarious condition of the world's fisheries is making ever-greater demands of the scientific assessment of fish stocks. Traditional assessments that rely on commercial catch statistics can have major shortcomings1 (as shown, for example, by the collapse of Canada's northern cod stock2), increasing the need for more fishery-independent data. Acoustic surveys can provide such information3, but ocean-going research vessels have high operating costs, and there is also widespread concern that fish avoid these vessels because of the noise they make, thereby biasing abundance estimates4. Here we present new data gathered by an autonomous underwater vehicle (AUV) showing that vessel avoidance is not a significant source of bias. Our investigation also heralds the arrival of AUVs as effective survey platforms.

A Mark-Recapture Experiment on Queen Scallops, Aequ1Pecten Opercularis, on a North Irish Sea Fishing Ground

A single-season mark-recapture experiment was carried out on queen scallops, Aequipecten opercularis (L.) (Bivalvia: Pectinidae) to assess the suitability of the technique for estimating population sizes and mortality rates of exploited populations. Tag-loss and tagging-induced mortality were 7.7% and 11.9% respectively. Non-reporting was negligible.In a single fishing season (June-December 1989) 25.4% of releases were recaptured alive. Mean density of commercial-sized queens was estimated as 0.47 m−2 over the fishing ground. Instantaneous rates of total (Z), fishing (F) and-natural (M) mortality, calculated from the monthly decline of recaptures during the fishing season, were 0.;41,0.21 and 0.20 per month respectively. The calculated M is very high but includes non-yield or indirect fishing mortality. Analysis of the age-frequency distribution of queens from an adjacent, largely unexploited, area indicated an M of only 0.036 per month (0.43 y−1). There was some indication of an increase in M in older year classes, associated with senescence.The mark-recapture methodology used here is suitable for this species, but single-release experiments place too much reliance on commercial catch-statistics.

The commercial fishery for and population dynamics of red crabGeryon maritaeoff South West Africa, 1976–1986

Commercial catch statistics for red crab Geryon maritae caught off South West Africa (Namibia) since 1980 and some historical data for the previous four years showed that crabs were much smaller in the northern areas than in the south. Catch per unit effort (cpue) was aseasonal and unaffected by soaking times of 24–120 h. Catches decreased from north to south, little fishing therefore taking place south of 22°S. Total catches increased from 1980, reaching a peak of over 10 000 tons (whole crab mass) in 1983, but subsequently falling to 7 000–8 000 tons between 1984 and 1986. Cpue, too, has decreased in recent years. The current size at first entry to the fishery is below that at which females mature, a situation which could lead to overfishing of the spawner stock. Analyses of yield per recruit for males (assuming instantaneous natural mortality rates of 0,05, 0,10 and 0,15) have shown that the present age at first capture is considerably less than that at which the yield for that sex would theoretically ...

Increased Catchability of the Deep Monofilament Nylon Gillnet and Its Expression in a Simulated Fishery

During 1979–81, Lake Huron fishermen changed from using 36-mesh monofilament nets to deeper (50-mesh) nets in the commercial fishery for lake whitefish (Coregonus clupeaformis). Simultaneous catch comparisons between the two gears showed that overall, deep nets were 1.7 times more efficient (but varied seasonally) for whitefish. The increase in efficiency exceeded that expected from the increase in area of the deeper nets. Simulation modeling demonstrates that the expression of enhanced catchability of deep nets is inversely proportional to the intensity of the fishery and thus total mortality rates (Z). Further, the temporal distribution of yield to the fishery would be advanced within the fishing period. This most recent change in catchability has introduced further bias in commercial catch and effort statistics.

The biology of the catfish Cnidoglanis macrocephalus (Plotosidae) in an Australian estuary

This paper describes the age structure, growth, diet and aspects of gonadal development in the cobbler, Cnidoglanis macrocephalus (Valenciennes), in the large Swan estuary in south-western Australia between August 1982 and June 1984. Analysis of otolith annuli showed that while the 0+ to 3+ age classes were regularly represented in monthly samples, the 4+ and more particularly the 5+ and 6+ were much less abundant. The weighted means for the back calculated lengths at the end of the first to fourth years of life were 181 mm (≡ 26 g), 314 mm (≡ 156 g), 418 mm (≡ 410 g) and 518 mm (≡ 833 g) respectively. The mean length at the end of the second year of life was similar to the minimum legal size for capture by commercial fishermen (320 mm). The von Bertlanffy growth curve calculated from the back calculated lengths was L t = 917 [1 − e −0·20( t + 0·11) ]. The relative weight of mulluscs, crustaceans and polychaetes in the intestine varied markedly between small and large fish, apparently reflecting differences in the size of these prey. The large mean diameter of mature eggs ( x=7·4 mm ) was correlated with a low mean absolute fecundity (2078). Trends shown by egg size, gonadosomatic index and time of appearance of spent females indicate that spawning takes place between October and December. The attainment of sexual maturity is both age- and size-dependent. Although sexually maturing and occasionally spent fish were found in the lower estuary, meristic values, commercial catch statistics and other data indicate that the cobbler found in the Swan estuary are part of a population which typically spawns at sea.

Distribution and abundance of freshwater eels (Anguilla spp.) in Tasmania

The distribution of A. australis australis Richardson and A. reinhardtii Steindachner in Tasmania was determined from electrofishing surveys and commercial catch records. A. a. australis is abundant in coastal streams and extends far inland in the major drainage systems to the main lakes in Tasmania's Central Highlands. Density and biomass estimates for A. a. australis in streams, <0.01-1 .40 m-2 and 0.04-23.01 g m-2, respectively, are similar to those recorded for A. australis schmidtii Phillipps in New Zealand and for A. anguilla L. in Europe, A. reinhardtii is restricted to coastal lagoons and the lower freshwater reaches and estuaries of streams in north-eastern Tasmania including Flinders Island. Substantial populations of A. reinhardtii reside in these areas (0.05 m-2, 114.66 g m-2 in Douglas River). Analysis of commercial catch statistics indicates that the initial eel yields from standing waterbodies were high in the 1960s by world standards, although landings and catch per unit effort have subsequently declined.

Relative Efficiency of Multifilament and Monofilament Nylon Gill Net Towards Lake Whitefish (Coregonus clupeaformis) in Lake Huron

In the early 1970s Lake Huron fishermen converted their gill nets from multifilament to monofilament nylon web in the lake whitefish (Coregonus clupeaformis) fishery. Catch comparisons in the two gears showed that monofilament nets were 1.8 times more efficient (but varied seasonally), resulting in biased commercial catch statistics. The use of monofilament web has probably increased exploitation pressure on whitefish. Both gears selected whitefish of the same size despite stock differences in individual size and shape. Catches in both gears declined during the full moon phase, possibly due to increased net visibility. Key words: mono-multifilament gillnet efficiency, selectivity, lunar illuminance, Coregonus clupeaformis, Lake Huron

Influence of Food Competition, Predation, and Cannibalism on Walleye (Stizostedion vitreum vitreum) and Sauger (S. canadense) Populations in Lake of the Woods, Minnesota

Feeding relationships between walleye, Stizostedion vitreum vitreum, and sauger, Stizostedion canadense, in Lake of the Woods, Minnesota, were investigated. Effectiveness of food consumption estimates in measuring feeding interactions was defined. Differences in walleye and sauger distribution, food habits, and feeding strata reduced interactions. Walleye feeding rate varied from 0.5 to 4.1% of body weight per day and was limited by prey abundance during June and July. Higher August and September prey densities did not influence walleye food consumption. Daily food consumption of sauger varied from 0.5 to 3.5% of body weight independent of changes in food availability. Relationships between the number of prey consumed daily by walleye and sauger and the decline in abundance of prey species suggested that predation was important in controlling food availability, and was the major cause of food competition and its limiting effect on walleye growth.Analysis of commercial catch statistics suggested that factors other than predation influenced walleye survival. However, the relationship between the number of young-of-the-year walleye consumed and their abundance in the lake demonstrated predation by sauger may be important to walleye survival.