Pelagic Fish Resources Research Articles

Visceral larvae as a predictive index of the overall level of fish batch infection in European anchovies (Engraulis encrasicolus): A rapid procedure for Food Business Operators to assess marketability

The European anchovy (Engraulis encrasicolus), one of the most important pelagic fish resources in the Mediterranean Sea, is frequently infected by anisakid larvae. Food Business Operators (FBOs) should use appropriate sampling plans and analytical methods to avoid commercialization of massively infected batches and reduce the risk of transmission of viable zoonotic larvae. In this study, performed at FishLab (Department of Veterinary Sciences of the University of Pisa) during 2016, an official sampling plan was associated with a digestion protocol for the inspection of anchovies. Considering that anisakid larvae are usually located in the fish visceral cavity and in the adjacent muscles (VM), this part was analyzed. In particular, we assessed the reliability of the digestion of a subsample of 150g (±30g) of VM, randomly collected from 29 specimens, in estimating the marketability of the anchovies' batch. Fifty-seven samples of 29 anchovies were collected. Each anchovy was sectioned to separate VM. All the subsamples were digested, and visible larvae counted. A high correlation between the number of larvae in VM regions and in the total batch was observed, indicating a very significant contribution of the VM region on total number of parasites. The Mean Abundance (MA) was used to assess the batch marketability according to a threshold calculated on the basis of the maximum number of nematodes tolerated per sample. Considering that the MA can be calculated only when the number of examined specimens is known, the number of visible Larvae per gram of tissue (LpG) was calculated on 150g (±30g) of VM subsamples. A LpG marketability threshold was calculated dividing the maximum number of tolerated nematodes by the average weight of a sample of 29 anchovies calculated considering data available in literature. To evaluate the diagnostic performance of the LpG threshold, the marketability of 57 batches assessed on the basis of the MA threshold was assumed as the gold standard. The proposed LpG showed very high Specificity and Sensitivity. These findings suggest that the analysis of VM is representative of the overall infestation of the batch, both when considering the absolute number of parasites and the LpG, and may represent a valid alternative to the whole anchovy digestion. In particular, the use of an automated digestive method, coupled with the aforesaid sampling plan, could allow the procedure to be used by FBOs in operational conditions.

Pola Rekrutmen, Mortalitas, dan Laju Eksploitasi Ikan Lemuru (Amblygaster sirm, Walbaum 1792) di Perairan Selat Sunda

Sunda Strait has high potential of pelagic fish resources, one of which is spotted sardinella (Amblygaster sirm). High market demand of spotted sardinella leads to its high exploitation. Management of sustainable used of this species need various biological information of the target species.The aims of this research wereto analyze of therecruitment pattern, mortality, and exploitation rate of spotted sardinella. Sampling was conducted in April to August 2015 from the catchment landed at Labuan Coastal Fishing Port, Banten. Fish samples taken during the study consisted of 527 males and 245 females. The results showed thatpeak recruitment season for spotted sardinella occurs in Maret (11.64%) and July (13.67%).The natural mortality (M), fishing mortality (F), total mortality (Z) for male were 0,33; 5,30; 5,63 year-1 respectively, and for female were 0,51; 7,75;8,27 year-1 respectively. Exploitation rate (E) for male was 0,94 year-1 and for female was 0,93 year-1.Keywords : exploitation, growth, mortality, spotted sardinella, Sunda Strait

Anticipated Effects of Climate Change on Coastal Upwelling Ecosystems

Ecosystem productivity in coastal ocean upwelling systems is threatened by climate change. Increases in spring and summer upwelling intensity, and associated increases in the rate of offshore advection, are expected. While this could counter effects of habitat warming, it could also lead to more frequent hypoxic events and lower densities of suitable-sized food particles for fish larvae. With upwelling intensification, ocean acidity will rise, affecting organisms with carbonate structures. Regardless of changes in upwelling, near-surface stratification, turbulent diffusion rates, source water origins, and perhaps thermocline depths associated with large-scale climate episodes (ENSO) maybe affected. Major impacts on pelagic fish resources appear unlikely unless couples with overfishing, although changes toward more subtropical community composition are likely. Marine mammals and seabirds that are tied to sparsely distributed nesting or resting grounds could experience difficulties in obtaining prey resources, or adaptively respond by moving to more favorable biogeographic provinces.

Analisis Depresiasi dan Kebijakan Pengelolaan Sumberdaya Ikan Layang di Wilayah Perairan Kota Ambon

Generally, fishery resources are open access which means that anyone can participate without having these resources. This is shown by an increase in the utilization of fish resources that will lead to a crisis in which when the rate of exploitation goes beyond the ability of regeneration that makes the catches more economical (economic overfishing). Moreover, this will take place in conditions of uncontrolled fishing. The main factor causing this crisis is the uncontrolled human intervention toward the existing fishery resources. The exploitation of these resources can lead to an imbalance between the input and the potential capture of fish resources so that it can lead to over-fishing, overcapacity, inefficiency arrest, resource rents decline, degradation of the resource stock and a decrease in production. The degradation impact of small pelagic fish resource, especially Layang fish in Ambon also is the reduction of producer welfare, especially the welfare of fishermen and coastal communities. This is due to, among others, the lack of control from the government as the authors,, and the lack of understanding of resource actors (local fishermen) about the nature of fish resources which are open access. Thus, the calculation of the depreciation of small pelagic fish resources, especially lyang fish, and welfare aspects which are considered important to know as a point of reference as well as an early warning signal to determine whether the extraction of small pelagic fish resources, especially layang fish in Ambon has exceeded their capabilities.

Controls of plankton production by pelagic fish predation and resource availability in the Alboran and Balearic Seas

A one-dimensional coupled physical and intermediate-complexity biochemical model comprising large and small phytoplankton and zooplankton groups, particulate organic nitrogen, ammonium and nitrate was developed to study the physical–biogeochemical interactions and parameters that control plankton production in the Alboran and Balearic Sea ecosystems. The model findings suggest that pelagic fish predation and resource availability through lateral and vertical nutrient inputs jointly characterize the plankton community structures. In agreement with previous observations, a typical annual plankton structure of the mesotrophic systems involves a vertically homogeneous biomass of large groups of phytoplankton and zooplankton within the upper 50-to-100m layer from mid-November to April and a subsurface biomass accumulation distributed roughly within 25–75m depths in the following months. Their light and temperature limitations constrain the smaller groups into the thermocline zone (25–50m) during late spring and summer. These obtained results were dependent on the zooplankton actively switching between preys (i.e., the food preference coefficients dependent on prey biomass). In the case of no switching, spurious dynamic equilibrium solutions may arise in the case of a constant and weak fish predation rate and using the quadratic predation formulation. The choice of a Holling Type II (i.e., hyperbolic) predation function may, however avoid ambiguous representation of the annual plankton structure in the case of a constant food preference choice under relatively weak predation pressures.

EXPLOITATION AND CPUE TREND OF THE SMALL PELAGIC FISHERIES IN THE SULAWESI SEA, INDONESIA

One of the expected benefits of the Sulu-Celebes Sea Project during its implementation is to have increased fish stocks at demonstration sites, as indicated by the Catch per Unit of Effort (CPUE). Analysis of catch and effort data of the small pelagic fisheries by using the surplus yield model was done to obtain information on the likely trend of CPUE for the last ten years. By using the pajeko as the standardized fishing gear the trend of CPUE has been calculated. Between 2000-2005, the trend of production (catch), effort and CPUE followed the general pattern of the exploited fisheries that already fully exploited, where the increasing trend of effort was not followed by the increasing catch. On the other hand, the trend of CPUE is decreased. In the following years, the trend of both catch and CPUE do not follow the general pattern of the exploited fisheries. The trend of catch, effort and CPUE has likely been stable, indicating that the fishery in this period has been leveled-off. The status of exploitation of the small pelagic fish resources in the Indonesian Sulawesi Sea is demermined by the MSY level that has likely been surpassed during the period 2003-2004. Therefore with the increasing effort in the following year the trend of catch was relatively stable. It is likely that the small pelagic fish stock in the Indonesian Sulawesi Sea might be ‘fully exploited’.

IDENTIFICATION OF FISHERY RESOURCES IN MADURA STRAIT BASED ON THE IMPLEMENTATION OF POTENTIAL FISHING ZONE INFORMATION FROM REMOTE SENSING

Spatial information of Potential Fishing Zone (PFZ) was used to identify the prospective location in the Madura Strait, where the fishermen from Fish Landing Port (FLP) around the Madura Strait conducted fishing activities. PFZ was aimed to determine fishing location, to identify the type of pelagic fish resources which were dominantly caught in the MAdura Strait. Fish resources data were obtained by observing the FLP in the east of Madura Strait especially in Pondok Mimbo, Jangkar, Besuki, Probolinggo, Pamekasan, and Sumenep. Based on the application of PFZ spatial information and observation, the types of pelagic fish caught on west monsoon were dominated by Euthynnus spp, Decapterus spp, Ratsrellinger spp, and Trichiurus spp. In the first transition season, types of fish resources were a mix between Euthynnus spp, Decapterus spp, Rastrellinger spp, Sardinella longiceps, and Trichiurus spp, however Sardinella longiceps were still dominated the catches. During the east monsoon fish resources at the Madura Strait was also dominated by Sardinella longiceps. This condition occurred until the second month of the second transition season followed by the mixing among Sardinella longiceps, Euthynnus spp, Decapterus spp, Rastrellinger spp and Trichiurus spp. Keywords: Fish Landing Port, NOAA-AVHRR, Potential fishing zone

The Global Competition for Wild Fish Resources between Livestock and Aquaculture

AbstractAquaculture satisfies a growing global demand for fish but also consumes an increasing share of the world’s wild fish resources. This has led to a concern that increased aquaculture production poses a threat to the sustainability of capture fisheries. We use a shrinkage estimator to estimate fishmeal demand from countries with different make‐up of meat and farmed salmon production. Although we are not able to identify structural differences between these sectors, the empirical results show that fishmeal demand is price inelastic. Technological change, however, is reducing fishmeal usage in feeds, suggesting that strong demand pressure on pelagic fish resources targeted for fishmeal is a temporary phenomenon.

Diet of sardine ( Sardinops sagax) in the northern Humboldt Current system and comparison with the diets of clupeoids in this and other eastern boundary upwelling systems

Sardines are one of the main small pelagic fish resources in eastern boundary upwelling systems (EBUS) where they play an important ecological role both as a predator of plankton and as prey of top predators. Sardine trophodynamics have been relatively well studied in three of the EBUS (the Benguela, California and Canary upwelling systems) but not in the Humboldt Current system. In this paper we describe the diet of sardine Sardinops sagax in the northern Humboldt Current system (NHCS) off Peru, using an analytical method which assesses relative dietary importance in terms of estimated prey carbon content. We assessed sardine diet by examining a total of 555 stomachs collected during six surveys conducted off Peru during the period 1996–1998, and compare our results with the diet of anchoveta Engraulis ringens off Peru and with the diets of sardines from the southern Benguela (also S. sagax) and the northern Canary ( Sardina pilchardus) upwelling systems. The diet of sardine off Peru is based primarily on zooplankton, similar to that observed for anchoveta but with several important differences. Firstly, sardine feed on smaller zooplankton than do anchoveta, with sardine diet consisting of smaller copepods and fewer euphausiids than anchoveta diet. Secondly, whilst phytoplankton represents <2% of sardine dietary carbon, this fraction is dominated by dinoflagellates, whereas diatoms are the dominant phytoplankton consumed by anchoveta. Hence, trophic competition between sardine and anchovy in the northern Humboldt Current system is minimized by their partitioning of the zooplankton food resource based on prey size, as has been reported in other systems. Whereas sardine in the NHCS feed on smaller zooplankton than do anchovy in that system, sardine in the NHCS forage on larger prey and obtain a substantial portion of their dietary carbon from euphausiids compared to sardine from the northern Canary and southern Benguela Current systems.

Assessment of the status of Lates stappersii (centropomidae) stock in lift-net fishery in Lake Tanganyika, Kigoma, Tanzania

An assessment of the status of Lates stappersii (Boulenger, 1914) stock in the lift-net fishery in Lake Tanganyika, Kigoma area, was carried out from January to December 2003. Results indicated that breeding is seasonal with peaks in February, July-August and December, and so was catch composition, with peaks in March, May and July–August that followed the abundance of its prey, Stolothrissa tanganicae . Catch per unit effort was similar between wet and dry seasons and peaked synchronously at all study sites probably as an indication of its abundance during those months; but also it could mean that the fishes were caught from the same general area. The unselective nature of the lift-net, a common fishing gear in the lake, could be exerting pressure on the pelagic resource, that leads to local over-fishing if not controlled. There is need to institute minimum fish size and mesh size limits and licensing, on a lake-wide basis, as fisheries management measures to safeguard against overexploitation of this highly variable and mobile yet important pelagic fish resource. Tanzania Journal of Science Vol. 32 (2) 2006: pp. 1-12

RESTORING PISCIVOROUS FISH POPULATIONS IN THE LAURENTIAN GREAT LAKES CAUSES SEABIRD DIETARY CHANGE

Ecosystem change often affects the structure of aquatic communities thereby regulating how much and by what pathways energy and critical nutrients flow through food webs. The availability of energy and essential nutrients to top predators such as seabirds that rely on resources near the water's surface will be affected by changes in pelagic prey abundance. Here, we present results from analysis of a 25-year data set documenting dietary change in a predatory seabird from the Laurentian Great Lakes. We reveal significant declines in trophic position and alterations in energy and nutrient flow over time. Temporal changes in seabird diet tracked decreases in pelagic prey fish abundance. As pelagic prey abundance declined, birds consumed less aquatic prey and more terrestrial food. This pattern was consistent across all five large lake ecosystems. Declines in prey fish abundance may have primarily been the result of predation by stocked piscivorous fishes, but other lake-specific factors were likely also important. Natural resource management activities can have unintended consequences for nontarget ecosystem components. Reductions in pelagic prey abundance have reduced the capacity of the Great Lakes to support the energetic requirements of surface-feeding seabirds. In an environment characterized by increasingly limited pelagic fish resources, they are being offered a Hobsonian choice: switch to less nutritious terrestrial prey or go hungry.

Changes in species composition and abundance of commercially important pelagic fish species in Kigoma area, Lake Tanganyika, Tanzania

The pelagic fishery of Lake Tanganyika provides employment to about 1 million consumers and protein to many more people living around the lake. It is mainly based on three commercially important fish species namely two clupeids Stolothrissa tanganicae and Limnothrissa miodon commonly known as “dagaa” and a perch Lates stappersii. A declining trend of the perch both in its composition and abundance in the pelagic fish landings is partly tied to local over-fishing and climate change. There are three important periods in the exploitation process identified as: (1) a traditional fishery period, the pre-1975 period marked by low catches of Lates spp. and a dominance of clupeids; (2) an industrial fishery period (1975–1978) marked by high catches of Lates stappersii and high total landings; and (3) an artisanal fishery period (post 1984) with relatively low catches and high dominance of clupeids especially Stolothrissa tanganicae. Population growth and refugee influx from the politically volatile Burundi and Democratic Republic of Congo both caused high fish protein demand, particularly for dried clupeids. Also changes in the rural economy caused by drought in the area are resulting into high exploitation pressure on the pelagic resources. Concerted efforts to prevent/reduce exploitation pressure on the pelagic fish resources should take into action a lake wide management strategy where by management issues in all the riparian countries should be harmonized. More effort should be geared towards preventing the use of beach seines and small meshed nets subsequently ensuring a sustainable utilization of the pelagic fish resources.

The role of pelagic fish as forage for the demersal fish community in the southern Bay of Biscay

The small pelagic fish represents the link between nekton and demersal communities, and they are an important food source for some demersal fish species. In the autumns between 1993 and 2002, 74,869 stomach contents of 25 demersal fish species were analysed during the scientific surveys organized by the Instituto Español de Oceanografía. These species represent the demersal fish community of the southern Bay of Biscay. An important part of their diet (39% by volume) was composed of pelagic fish species (e.g. Engraulis encrasicolus, Gadiculus argenteus, Micromesistius poutassou, Trachurus trachurus, Sardina pilchardus, Scomber scombrus). Among all these prey species, the relevance of M. poutassou and G. argenteus stood out because of their high abundance both in the diets and during the scientific surveys. The relevance of pelagic fish as prey increased with predator size, reaching more than 60% of the diet by volume in the length range 25–29 cm. However, fish predators larger than 50 cm depended less on pelagic fish (33%), since they were also able to feed on other sources such as megafaunal invertebrates, mainly cephalopods. The pelagic fish resource was primarily exploited by 12 demersal fish species, with Merluccius merluccius and Zeus faber being the main ones feeding on small pelagics, which was related to the vertical movement of predators and prey through the water column. Survey abundance indices were used as indicators of prey abundance in the ecosystem, both for biomass and number. There was evidence for density-dependant feeding by predators on E. encrasicolus, G. argenteus and T. trachurus, while the main discrepancies between abundance in the stomachs and in the surveys were due to differential availability of prey length classes in the environment. Small prey species and individuals were exploited by most demersal fish while large prey species were less accessible to predators.

A knowledge base for management of the capital-intensive fishery for small pelagic fish off South Africa

As a contribution to South Africa's move towards an ecosystem approach to fisheries management, this study explores the existence of common perceptions about South Africa's pelagic fishery between resource users and scientists. It represents a collaborative research effort of social and natural scientists. A brief overview is given of the southern Benguela upwelling ecosystem and small pelagic fish resources, the fishery, and management of the fishery. Stakeholder knowledge and views were determined by conducting open-ended qualitative local knowledge interviews. Candidate indicators to address five major issues raised in the interviews were selected: length-at-50% maturity, total mortality, exploitation rate, proportion of bycatch, mean length of catch, and centre of gravity of catches. The indicator approach is shown to be a useful tool to manage the South African small pelagic fishery, and can be made compatible with existing management approaches. The foundation of a good adaptive fisheries management system is a data collection system that enables multi-disciplinary analysis and provides a basis on which decisions can be made.

Small pelagics in upwelling systems: patterns of interaction and structural changes in “wasp-waist” ecosystems

In upwelling ecosystems, there is often a crucial intermediate trophic level, occupied by small, plankton-feeding pelagic fish dominated by one or a few schooling species. Their massive populations may vary radically in size under intensive exploitation. We have used decadal-scale time series to explore patterns of interactions between these fish, their prey, and their predators so as to quantify functional roles of small pelagic fish in those ecosystems. Top-down control of zooplankton is detected off South Africa, Ghana, Japan, and in the Black Sea. Conversely, bottom-up control of predators, such as predatory fish and marine birds, is observed in the Benguela, Guinea, and Humboldt currents. Thus small pelagic fish exert a major control on the trophic dynamics of upwelling ecosystems and constitute midtrophic-level “wasp-waist” populations. Ecosystem effects of fishing are addressed by considering potential structural changes at different scales of observation, ranging from individuals, via school dynamics, to food webs. The overall impact is explored using a trophic model (Ecosim) given different types of food web control. Ecosystem dynamics can be entirely different depending on how the food web is controlled (bottom-up, top-down or wasp-waist). The threat of eroding intra-specific diversity is emphasized because it may lead to a long-term decline in the productivity of the pelagic fish resources. School composition is shown to reflect the relative species abundance within the pelagic community and functions as a “school trap” that could maintain a collapsed population in a depleted state for lengthy periods, and affect spatial dynamics such as migrations. As a result, overfishing can alter the abundance, composition, and distribution in pelagic communities, and may induce drastic changes of state. Predation on zooplankton by the jack mackerel (Trachurus symmetricus murphyi) population in the South Pacific provides an example of the alteration of matter fluxes in trophic webs caused by fishery removals. In conclusion, it is doubtful that pelagic fisheries will continue to increase without major disruptions to ecosystems.

Invasion of the Black Sea by the ctenophore Mnemiopsis leidyi and recent changes in pelagic community structure

A short synthesis of the present state of the ctenophore, Mnemiopsis leidyi, invasion in the Black Sea is given, together with a brief review of its status in other areas of the Mediterranean basin. The impact of M. leidyi on the main components of the pelagic community, mesozooplankton, ichthyoplankton and fish resources, based on published data and new field studies (1992–1997) are analysed. This assessment showed sharp fluctuations in the interannual abundance of M. leidyi. The main factors controlling the spatial distribution of M. leidyi were temperature and, to a lesser degree, salinity, whereas its abundance was controlled by food availability. An analysis of the main constituents of the pelagic ecosystem of the Black Sea before the M. leidyi outbreak showed that a reduction in numbers of planktivorous fishes, the main competitors of M. leidyi, could be a possible reason for the upsurge in abundance of M. leidyi. Following the increase of M. leidyi, there was a decline in the abundance and species diversity of ichthyoplankton and mesozooplankton. An assessment of data collected during the period 1992–1997 showed that the number of fish eggs and larvae and of zooplankton was negatively related to M. leidyi abundance. After the recent decrease of M. leidyi in the period 1995–1997, there has been an increase in abundance and diversity of fish eggs, fish larvae, and zooplankton, which together with an increased catch of planktivorous fish indicates that there has been a recovery of the ecosystem.

Acoustic methods applied to fish environmental studies in the Baltic Sea

Acoustic methods can play an important role in studies of fish group behaviour in relation to environmental factors. This paper presents new approaches to treating acoustic, biological and hydrological data collected during surveys of pelagic fish resources in the Baltic Sea. It must be underlined that the Baltic ecosystem is characterized by low salinities (2–20 PSU) and a two-layer structure. A method of macrosounding, giving for single transects a graphic visualization of current spatial gradients in fish distribution in macro-scale was enriched by adding the overall community structure (e.g., temperature, salinity, oxygen, etc.), expressed by appropriate isolines. A more developed version, called `matrix macrosounding', designed for description of cross-sections, characteristic for the Baltic ecosystem, structured in the form of elementary rectangles (matrix elements), is introduced and examples of its application for short-term or long-term ecological studies are given. Basic diel fish environmental preferences were estimated by correlating acoustic and hydrological data collected over the period 1981–1996 in the southern Baltic. Preliminary models of day life-cycle of fish in relation to main environmental factors were then formulated, and applied to fish behavioural studies. Examples of fish behaviour models, determined for the autumn, are shown.

ECHOBASE—A portable geographic fishery research database system

A geographic fishery research database system (GFRDBS), called ECHOBASE, for storing and management of data on pelagic fish resources from acoustic surveys and catch samples, combined with environmental data in a geographic context, has been developed. The system constitutes a portable and inexpensive yet powerful tool for fishery research and environmental monitoring and provides on‐board data processing and mapping capabilities. Data are acquired from an echosounder, echo signal processor, environmental profiler (CTD probe), and Global Positioning System (GPS) receiver. The electronic digitized maps (based on C‐MAP public format files) provide active on‐screen nautical charts. The basic GFRDBS platform is a portable PC 486 machine, which is used as an on‐board data acquisition and processing tool running under MS Windows 3.1 operating environment. The system is designed around the Borland's PARADOX package, which provides a relational database for managing acoustic, catch, and environmental data. The EC...

The role of acoustic surveys in the assessment of pelagic fish resources on the South African continental shelf

Acoustic data on the abundance and distribution of anchovy Engraulis capensis, pilchard Sardinops ocellatus and round herring Etrumeus whiteheadi on the South African continental shelf have been collected from 21 echo-integrator surveys between 1984 and 1991. Most effort has been concentrated on estimating adult biomass of anchovy and pilchard in November (spring) and anchovy recruitment in autumn. Distribution maps from all surveys are presented and the biomass estimates considered most reliable documented. A series of distribution maps tracing movements of three anchovy year-classes over a four-year period is presented to illustrate the usefulness of the surveys in migration studies. The major findings of the survey programme have been that anchovy are generally considerably more abundant and widespread than was thought to be the case prior to the surveys, that the pilchard resource has recovered substantially in recent years, and that the round herring resource, about which little was known prior to th...

Distribution of the pelagic fish populations on the continental shelf off the Gulf of Bintuni (Irian Jaya, Indonesia)

In july 1983, the French R.V. ‘Coriolis’ carried out an acoustic survey between Irian Jaya, Misool Island and Seram Island. One of the aims of the cruise was a study on the distribution of the pelagic fish resources on the large shelf off the Gulf of Bintuni, between 1°S and 3°S and from 130°E to 132°E. The cruise took place during the southeast monsoon. The fish traces recorded were distributed into three distinct groups: coastal fish populations up to the 30 m isobath, offshore fish populations near the shelf edge, coastal tuna shoals in the large channel that separates Misool Island from Irian Jaya. These fish showed a different behaviour between day and night. The total biomass, probably underestimated due to the impossibility of sampling the fish recordings, came to 89 000 tonnes in the area surveyed.