This paper focuses on the transition in the Dutch cutter fleet-targeting flatfish, from the conventional beam trawl to the pulse trawl fishing gear. In doing so, we explore the process of gear transition, presenting the challenges that fishers and policy-makers face. The pulse trawl technique represents a particularly controversial gear transition as it makes use of electricity, which has been banned by the European Union since 1988. However, it is seen by those developing it in the Netherlands as an important alternative fishing gear to the conventional beam trawl technique, which is becoming increasingly inefficient with rising fuel prices and well-documented impact on benthic habitats. By using a multi-level perspective on socio-technical transitions as the analytical framework, we explore the development of the pulse trawl and the interaction between different levels. We also discuss the influence of technology-push on its transition into practice and regulation. This paper demonstrates the importance of social dimensions in the adoption of new fishing gears and in doing so contributes to our knowledge on how technological transitions in fisheries can be managed.
The purse-seine tuna fleet in the Western Pacific Ocean has undergone an accelerated expansion since the 1980s. The fishery is primarily managed using fishing effort limits. Constraining effort to ensure the biological health of the stock, while enhancing economic benefits generated by the fishery, is a major challenge faced by fisheries managers in this region. To maintain effort levels that achieve those objectives, there is a need to take into account technical and efficiency changes over time that influence the productivity of fleets. This study evaluates how the productivity of four of the region's purse-seine fleets has changed year on year between 1993 and 2010 using a robust bootstrapped Malmquist index approach. This index is separated into: technical change, which represents the change in productivity due to the introduction of new technology and efficiency change, the change in productivity resulting from a change in the level of efficiency in the use of inputs. The results show that half of the 56 purse-seine vessels examined displayed significant gains in productivity, which appeared to be driven primarily by technical change. The technical efficiency of fleets showed less marked changes, potentially due to the practical inability to maximize performance in the face of dramatic technological advances.
Microplastics in the marine environment are well documented, and interactions with marine biota have been described worldwide. However, interactions with vertically migrating fish are poorly understood. The diel vertical migration of mesopelagic fish represents one, if not the largest, vertical migration of biomass on the planet, and is thus an important link between the euphotic zone, transporting carbon and other nutrients to global deep sea communities. Knowledge of how mesopelagic fish interact and distribute plastic as a marine contaminant is required as these populations have been identified as a potential global industrial fishery for fishmeal production. Ingestion of microplastic by mesopelagic fish in the Northeast Atlantic was studied. Approximately 11% of the 761 fish examined had microplastics present in their digestive tracts. No clear difference in ingestion frequency was identified between species, location, migration behaviour, or time of capture. While ingesting microplastic may not negatively impact individual mesopelagic fish, the movement of mesopelagic fish from the euphotic zone to deeper waters could mediate transfer of microplastics to otherwise unexposed species and regions of the world's oceans.
This study provides an inventory of the recent benthic macrofaunal communities in the entire Baltic Sea. The analyses of soft-bottom benthic invertebrate community data based on over 7000 locations in the Baltic Sea suggested the existence of 10 major communities based on species abundances and 17 communities based on species biomasses, respectively. The low-saline northern Baltic, characterized by silty sediments, is dominated by Monoporeia affinis, Marenzelleria spp., and Macoma balthica. Hydrobiidae, Pygospio elegans, and Cerastoderma glaucum dominate the community in sandy habitats off the Estonian west coast and in the southeastern and southern Baltic Sea. Deep parts of the Gulf of Finland and central Baltic Sea often experience hypoxia, and when oxygen levels in these regions recover, Bylgides sarsi was the first species to colonize. The southwestern Baltic Sea, with high salinity, has higher macrofaunal diversity compared with the northern parts. To spatially interpolate the distribution of the major communities, we used the Random Forest method. Substrate data, bathymetric maps, and modelled hydrographical fields were used as predictors. Model predictions were in good agreement with observations, quantified by Cohen's κ of 0.90 for the abundance and 0.89 in the wet weight-based model. Misclassifications were mainly associated with uncommon classes in regions with high spatial variability. Our analysis provides a detailed baseline map of the distribution of benthic communities in the Baltic Sea to be used both in science and management.
Floating fish farm installations attract a number of marine species, probably because they provide both shelter and excess feed from the cages. Saithe are by far the most numerous fish visitors to fish farms on the Norwegian coast, and may gather in large numbers beneath the cages, but detailed knowledge of their swimming behaviour is limited. This study examined the vertical movements and distribution of saithe equipped with acoustic transmitters at 15 fish farms over a period of almost 2 years. The saithe aggregating around fish farms displayed behavioural patterns reported from saithe elsewhere; diel rhytms in vertical distribution, reduced activity level at night and seasonality in swimming depth. Typical residence depth was from 25 to 50 m in summer and 60 to 90 m during winter. However, an anomaly was observed, as fish moved 10–20 m closer to the surface during mid-winter. The reason for this is not known, but may be associated with the use of artificial light to illuminate the fish farm sea cages. The fish were usually distributed through ∼100 m of the water column. In 38% of the observations, there was no apparent diel vertical migration pattern, but 46% of the data showed fish either moved up or down during the daylight hours. Interindividual and intersite variability, in preferred night-resting depth, is a possible explanation for the differing vertical migratory patterns. Fish also moved away from fish farms in daytime (16% of all observations), probably to feed elsewhere. The results suggest that saithe establish core residence areas close to fish farms.
Atlantic menhaden, Brevoortia tyrannus, is an abundant, schooling pelagic fish that is widely distributed in the coastal Northwest Atlantic. It supports the largest single-species fishery by volume on the east coast of the United States. However, relatively little is known about factors that control recruitment, and its stock–recruitment relationship is poorly defined. Atlantic menhaden is managed as a single unit stock, but fisheries and environmental variables likely act regionally on recruitments. To better understand spatial and temporal variability in recruitment, fishery-independent time-series (1959–2013) of young-of-year (YOY) abundance indices from the Mid-Atlantic to Southern New England (SNE) were analysed using dynamic factor analysis and generalized additive models. Recruitment time-series demonstrated low-frequency variability and the analyses identified two broad geographical groupings, the Chesapeake Bay (CB) and SNE. Each of these two regions exhibited changes in YOY abundance and different periods of relatively high YOY abundance that were inversely related to each other; CB indices were highest from ca. 1971 to 1991, whereas SNE indices were high from ca. 1995 to 2005. We tested for effects of climatic, environmental, biological, and fishing-related variables that have been documented or hypothesized to influence stock productivity. A broad-scale indicator of climate, the Atlantic Multidecadal Oscillation, was the best single predictor of coast-wide recruitment patterns, and had opposing effects on the CB and SNE regions. Underlying mechanisms of spatial and interannual variability in recruitment likely derive from interactions among climatology, larval transport, adult menhaden distribution, and habitat suitability. The identified regional patterns and climatic effects have implications for the stock assessment of Atlantic menhaden, particularly given the geographically constrained nature of the existing fishery and the climatic oscillations characteristic of the coastal ocean.
Annual spatial distribution and relative abundance of age-2 and age-3 northern rock sole (Lepidopsetta polyxystra) and summer bottom temperatures were analysed using data from eastern Bering Sea summer trawl surveys from 1982 through 2012. Previously observed differences in age-0 northern rock sole distribution persisted until age-2 and age-3. Latitudinal distributions of age-2 and age-3 fish were correlated most strongly with summer bottom temperatures 2 and 3 years prior to the survey year, during the time that the fish would have been age-0. Thus, temperature during the age-0 year may affect spatial distribution for the first few years of life. Distribution of age-2 and age-3 fish shifted northwards 2 years after the beginning of a warming trend from 1999 to 2003, and shifted southwards 2 years after a cooling trend from 2004 through 2010. Northerly distributions were correlated with high abundances. Density dependence was ruled out as a reason for northward shifts in distribution given a lack of correlation between latitudinal distributions and the annual abundances within the southern part of the distribution. We propose that the large northern nursery area produces large cohorts of northern rock sole, and that bottom temperatures in the age-0 year affect use of the northern nursery area.
Fisheries independent monitoring of widely distributed pelagic fish species which conduct large seasonal migrations is logistically complex and expensive. One of the commercially most important examples of such a species in the Northeast Atlantic Ocean is mackerel for which up to recently only an international triennial egg survey contributed to the stock assessment. In this study, we explore whether fisheries acoustic data, recorded opportunistically during the English component of the North Sea International Bottom Trawl Survey, can contribute to an improved understanding of mackerel distribution and provide supplementary data to existing dedicated monitoring surveys. Using a previously published multifrequency acoustic mackerel detection algorithm, we extracted the distribution and abundance of schooling mackerel for the whole of the North Sea during August and September between 2007 and 2013. The spatio-temporal coverage of this unique dataset is of particular interest because it includes part of the unsurveyed summer mackerel feeding grounds in the northern North Sea. Recent increases in landings in Icelandic waters during this season suggested that changes have occurred in the mackerel feeding distribution. Thus far it is poorly understood whether these changes are due to a shift, i.e. mackerel moving away from their traditional feeding grounds in the northern North Sea and southern Norwegian Sea, or whether the species' distribution has expanded. We therefore explored whether acoustically derived biomass of schooling mackerel declined in the northern North Sea during the study period, which would suggest a shift in mackerel distribution rather than an expansion. The results of this study show that in the North Sea, schooling mackerel abundance has increased and that its distribution in this area has not changed over this period. Both of these findings provide, to our knowledge, the first evidence in support of the hypothesis that mackerel have expanded their distribution rather than moved away.
Atlantic halibut (Hippoglossus hippoglossus) have a long history of exploitation in the Northwest Atlantic and have gone through several periods of high biomass followed by a population crash. An assessment model using data collected on the Scotian Shelf and southern Grand Banks shows that the population peaked in 1984, then decreased sharply to a low in 1993. Several management measures were taken during the decline, including reductions in total allowable catch and a minimum size limit. Concurrently, removals by the otter trawl fishery were drastically reduced following the collapse of the cod (Gadus morhua) fishery. In 2003, recruitment increased and continued to be high for 6 years. Fishing mortality rates were moderate in the late 1990s and 2000s and the population increased. By 2009, the Atlantic halibut population was highly productive with both high biomass and high levels of recruitment. The coincidence in the timing of population recovery and management actions indicates that effective management contributed to the recovery of Atlantic halibut.
The Ecosystem Approach to Fisheries Management claims that fisheries management should take into account the ecosystem processes; in that context, it is useful to examine the functional traits of fisheries assemblages. This can be a challenge in multispecies fisheries. We used 21 biological traits of 86 species to investigate the relationship between-species and trait composition and to identify species with rare functional traits. Combining these traits with two catch datasets from the eastern Mediterranean (Patraikos Gulf: small-scale fleet, eastern Ionian Sea: entire multispecies fleet), we investigated whether certain fishing tactics or gears tend to remove specific traits, using multivariate methodologies. Species and traits composition of the catches were related, but an important part of trait variability was not explained by species composition. Rare traits and trait combinations were found for important target or bycatch species. Differences in the traits composition of fishing operations were revealed both between fishing tactics (Patraikos) as well as gears and areas (eastern Ionian); hierarchical clustering and MDS indicated the distinction of purse-seine catches at gear level. SIMPER analysis by trait indicated associations of certain trait categories mainly with purse-seines (at gear level) and longline métiers and a trammel-net métier (at métier level). The identification of rare traits or their combinations can have significant management implications as overfishing of the species with these traits could result in altering assemblage functioning. It seems that the multispecies character of the benthic fisheries results in a balanced trait removal, while management should regulate the effects of purse-seine fisheries on the fisheries assemblage functioning. Further investigation of the functions that fishing may remove from the ecosystem could contribute to understanding the effects of fishing and reveal overlooked aspects useful for the improvement of fisheries management.