Exploring the use of neural networks for biomass forecasts in the Peruvian upwelling ecosystem

A pilot study was conducted to study the ability of an artificial neural network to predict the biomass of Peruvian anchoveta Engraulis ringens, given time series of earlier biomasses, and of environmental parameters (ocenographic data and predator abundances). Acceptable predictions of three months or more appear feasible after thorough scrutiny of the input data set.

Length-weight relationships for some important forage crustaceans from South Africa

The diet of marine animals is usually determined by stomach content analysis. Although partially digested prey fragments can often be identified to species level, it is difficult to estimate the original mass of the prey organism. This information, however, is essential for calculating both the total food intake as well as the relative contribution of each prey item. In this study we present regression equations that can be used to estimate the original mass of 18 common South African crustaceans from various indigestible fragments such as the carapace (length and width), chelae (length and width of left and right dactylus) and eye (length and width).

Improvement of traditional shrimp culture in the Mekong Delta

Improvements to traditional brackishwater shrimp culture in the Mekong Delta, Vietnam are discussed. A technical support program has been implemented based on a so-called improved extensive shrimp culture method, as previously developed and tested by the Artermia and Shrimp Research and Development Center (ASRDC). The program focuses on: 1) the use of hatchery-produced postlarvae (of Penaeus monodon and P. merguinensis) nursed for three to four weeks, and 2) the application of low-cost pond management practices including predator control, supplementary feeding and frequent water renewal. A credit program, managed as a revolving fund was made available. A dialogue among participating farmers was encouraged through the organization of group meetings before and after each production cycle.

The small pelagic Rastrineobola argentea: successful survivor in Lake Victoria

The small cyprinid dagaa (Rastreneobola argentea) is the only indigenous species from Lake Victoria which still supports an important fishery after the population boom of the introduced Nile perch (Lates niloticus), while at the same time it is a major prey species of the perch. The observed life-history tactics and the shift from juvenile to adult exploitation mortality made dagaa a successful survivor in a disrupted ecosystem. Although the prospects for a sustainable fishery are good, the current increase in the use of mosquito seines is dangerous. Not only do mosquito seines yield a lower catch per unit of effort than alternative gear, but they also show a strong selection for juvenile dagaa.

Impact of the California sea lion (Zalophus californianus) on salmon fisheries in Monterey Bay, California

To assess the impact of California sea lions (Zalophus californianus) on salmon fisheries in the Monterey Bay region of California, the percentages of hooked fish taken by sea lions in commercial and recreational salmon fisheries were estimated from 1997 to 1999. Onboard surveys of sea lion interactions with the commercial and recreational f isheries and dockside interviews with fishermen after their return to port were conducted in the ports of Santa Cruz, Moss Landing, and Monterey. Approximately 1745 hours of onboard and dockside surveys were conducted—924 hours in the commercial fishery and 821 hours in the recreational fishery (commercial passenger fishing vessels [CPFVs] and personal skiffs combined). Adult male California sea lions were responsible for 98.4% of the observed depredations of hooked salmon in the commercial and recreational fisheries in Monterey Bay. Mean annual percentages of hooked salmon taken by sea lions ranged from 8.5% to 28.6% in the commercial fishery, 2.2% to 18.36% in the CPFVs, and 4.0% to 17.5% in the personal skiff fishery. Depredation levels in the commercial and recreational salmon fisheries were greatest in 1998—likely a result of the large El Niño Southern Oscillation (ENSO) event that occurred from 1997 to 1998 that reduced natural prey resources. Commercial fishermen lost an estimated $18,031−$60,570 of gear and $225,833−$498,076 worth of salmon as a result of interactions with sea lions. Approximately 1.4−6.2% of the available salmon population was removed from the system as a result of sea lion interactions with the fishery. Assessing the impact of a growing sea lion population on fisheries stocks is difficult, but may be necessary for effective fisheries management.

Survey- and fishery-derived estimates of Pacific cod (Gadus macrocephalus) biomass: implications for strategies to reduce interactions between groundfish fisheries and Steller sea lions (Eumetopias jubatus)

Survey- and fishery-derived biomass estimates have indicated that the harvest indices for Pacific cod (Gadus macrocephalus) within a portion of Steller sea lion (Eumetopias jubatus) critical habitat in February and March 2001 were five to 16 times greater than the annual rate for the entire Bering Sea-Aleutian Islands stock. A bottom trawl survey yielded a cod biomass estimate of 49,032 metric tons (t) for the entire area surveyed, of which less than half (23,329 t) was located within the area used primarily by the commercial fishery, which caught 11,631 t of Pacific cod. Leslie depletion analyses of fishery data yielded biomass estimates of approximately 14,500 t (95% confidence intervals of approximately 9,000–25,000 t), which are within the 95% confidence interval on the fished area survey estimate (12,846–33,812 t). These data indicate that Leslie analyses may be useful in estimating local fish biomass and harvest indices for certain marine fisheries that are well constrained spatially and relatively short in duration (weeks). In addition, fishery effects on prey availability within the time and space scales relevant to foraging sea lions may be much greater than the effects indicated by annual harvest rates estimated from stock assessments averaged across the range of the target spec

Seasonal marine growth of Bristol Bay sockeye salmon (Oncorhynchus nerka) in relation to competition with Asian pink salmon (O. gorbuscha) and the 1977 ocean regime shift

Recent research demonstrated significantly lower growth and survival of Bristol Bay sockeye salmon (Oncorhynchus nerka) during odd-numbered years of their second or third years at sea (1975, 1977, etc.), a trend that was opposite that of Asian pink salmon (O. gorbuscha) abundance. Here we evaluated seasonal growth trends of Kvichak and Egegik river sockeye salmon (Bristol Bay stocks) during even- and odd-numbered years at sea by measuring scale circuli increments within each g rowth zone of each major salmon age group between 1955 and 2000. First year scale growth was not significantly different between odd- and even-numbered years, but peak growth of age-2 smolts was significantly higher than age-1. smolts. Total second and third year scale growth of salmon was significantly lower during odd- than during even-numbered years. However, reduced scale growth in odd-numbered years began after peak growth in spring and continued through summer and fall even though most pink salmon had left the high seas by late July (10−18% growth reduction in odd vs. even years). The alternating odd and even year growth pattern was consistent before and after the 1977 ocean reg ime shift. During 1977−2000, when salmon abundance was relatively great, sockeye salmon growth was high during specific seasons compared with that during 1955−1976, that is to say, immediately after entry to Bristol Bay, after peak growth in the first year, during the middle of the second growing season, and during spring of the third season. Growth after the spring peak in the third year at sea was relatively low during 1977−2000. We hypothesize that high consumption rates of prey by pink salmon during spring through mid-July of odd-numbered years, coupled with declining zooplankton biomass during summer and potentially cyclic abundances of squid and other prey, contributed to reduced prey availability and therefore reduced growth of Bristol Bay sockeye salmon during late spring through fall of odd-numbered years.

Distribution, feeding condition, and growth of Japanese Spanish mackerel (Scomberomorus niphonius) larvae in the Seto Inland Sea

Distribution of eggs and larvae and feeding and growth of larvae of Japanese Spanish mackerel (Scomberomorus niphonius) were investigated in relation to their prey in the Sea of Hiuchi, the Seto Inland Sea, Japan, in 1995 and 1996. The abundance of S. niphonius eggs and larvae peaked in late May, corresponding with that of clupeid larvae, the major prey organisms of S. niphonius larvae. The eggs were abundant in the northwestern waters and the larvae were abundant in the southern waters in late May in both years, indicating a southward drift during egg and yolksac stages by residual f low in the central part of the Sea of Hiuchi. Abundance of clupeid larvae in southern waters, where S. niphonius larvae were abundant, may indicate a spawning strategy on the part of first-feeding S. niphonius larvae to encounter the spatial and temporal peak in ichthyoplankton prey abundance in the Seto Inland Sea. Abundance of the clupeid larvae was higher in 1995 than in 1996. Feeding incidence (percentage of stomachs with food; 85.3% in 1995 and 67.7% in 1996) and mean growth rate estimated from otolith daily increments (1.05 mm/d in 1995 and 0.85 mm/d in 1996) of S. niphonius larvae in late May were significantly higher in 1995. Young-of-the-year S. niphonius abundance and catch per unit of fishing effort of 1-year-old S. niphonius in the Sea of Hiuchi was higher in 1995, indicating a more successful recruitment in this year. Spatial and temporal correspondence with high ichthyoplankton prey concentration was considered one of the important determinants for the feeding success, growth, and survival of S. niphonius larvae.

Feeding habits of European hake (Merluccius merluccius) in the central Mediterranean Sea

European hake (Merluccius merluccius) is an important predator of deeper shelf-upper slope Mediterranean communities. It is a nectobenthic species distributed over a wide depth range (20−1000 m) throughout the Mediterranean Sea and the north east Atlantic region (Fisher et al., 1987). Notwithstanding the ecological and economic importance (Oliver and Massutí, 1995) of hake in the Mediterranean, many aspects of its biology (e.g., recruitment and reproduction), due to multiple spawning (Sarano, 1986) and the current state of exploitation, are poorly understood (Arneri and Morales-Nin, 2000).

Diet of oceanic loggerhead sea turtles (Caretta caretta) in the central North Pacific

Diet analysis of 52 loggerhead sea turtles (Caretta caretta) collected as bycatch from 1990 to 1992 in the high-seas driftnet fishery operating between lat. 29.5°N and 43°N and between long. 150°E and 154°W demonstrated that these turtles fed predominately at the surface; few deeper water prey items were present in their stomachs. The turtles ranged in size from 13.5 to 74.0 cm curved carapace length. Whole turtles (n =10) and excised stomachs (n= 42) were frozen and transported to a laboratory for analysis of major faunal components. Neustonic species accounted for four of the five most common prey taxa. The most common prey items were Janthina spp. (Gastropoda); Carinaria cithara Benson 1835 (Heteropoda); a chondrophore, Velella velella (Hydrodia); Lepas spp. (Cirripedia), Planes spp. (Decapoda: Grapsidae), and pyrosomas (Pyrosoma spp.).

Geographic variation among age-0 walleye pollock (Theragra chalcogramma): evidence of mesoscale variation in nursery quality?

Nurseries play an important part in the production of marine f ishes. Determining the relative importance of different nurseries in maintaining the parental population, however, can be difficult. In the western Gulf of Alaska, the Kodiak Island vicinity may be particularly well suited as a pollock nursery because of a prey-rich nearshore environment. Our objectives were 1) to examine age-0 pollock body condition, growth, and diet for evidence of a nearshore-shelf effect, and 2) to determine if variation in the potential prey field of zooplankton was associated with this effect. This was a pilot study that occurred in three bays and over the adjacent shelf off east Kodiak Island during 5−18 September 1993. Sampling occurred only during night at locations where echo sign indicated the presence of age-0 pollock. Echo sign was targeted to increase the chance of collecting fish given the limited vessel time. Fish condition was indicated by length-specific body weight. Growth rate indices were estimated for three different periods by using fish lengthage data and daily otolith increment widths: 1) from hatching date to capture, 2) 1−5 d before capture, and 3) 6−10 d before capture. Fish diet was determined from gut content analysis. Considerable variation among areas was evident in zooplankton composition, and fish condition, growth, and diet. However, relatively high prey densities, as well as fish condition and growth rates indicated that Chiniak Bay was particularly well suited as a pollock nursery. Hatching-date distributions indicated that most of the age-0 walleye pollock from bays were spawned earlier than were those from the shelf. The benefit of being reared in nearshore areas is therefore realized more by individuals that were spawned early than by individuals spawned relatively late.

Tagging studies on the jumbo squid (Dosidicus gigas) in the Gulf of California, Mexico

Dosidicus gigas, the only species in the genus Dosidicus, is commonly known as the jumbo squid, jumbo flying squid (FAO, see Roper et al., 1984), or Humboldt squid. It is the largest ommastrephid squid and is endemic to the Eastern Pacific, ranging from northern California to southern Chile and to 140oW at the equator (Nesis, 1983; Nigmatullin, et al., 2001). During the last two decades it has become an extremely important fisheries resource in the Gulf of California (Ehrhardt et al., 1983; Morales-Bojórquez et al., 2001), around the Costa Rica Dome (Ichii et al., 2002) and off Peru (Taipe et al., 2001). It is also an active predator that undoubtedly has an important impact on local ecology in areas where it is abundant (Ehrhardt et al., 1983; Nesis, 1983; Nigmatullin et al., 2001; Markaida and Sosa-Nishizaki, 2003).

Ecosystem-based Management for Protected Species in the North Pacific Fisheries

In the North Pacific Ocean, an ecosystem-based fishery management approach has been adopted. A significant objective of this approach is to reduce interactions between fishery-related activities and protected species. We review management measures developed by the North Pacific Fishery Management Council and the National Marine Fisheries Service to reduce effects of the groundfish fisheries off Alaska on marine mammals and seabirds, while continuing to provide economic opportunities for fishery participants. Direct measures have been taken to mitigate known fishery impacts, and precautionary measures have been taken for species with potential (but no documented) interactions with the groundfish fisheries. Area closures limit disturbance to marine mammals at rookeries and haulouts, protect sensitive benthic habitat, and reduce potential competition for prey resources. Temporal and spatial dispersion of catches reduce the localized impact of fishery removals. Seabird avoidance measures have been implemented through collaboration with fishery participants and have been highly successful in reducing seabird bycatch. Finally, a comprehensive observer monitoring program provides data on the location and extent of bycatch of marine mammals and seabirds. These measures provide managers with the flexibility to adapt to changes in the status of protected species and evolving conditions in the fisheries. This review should be useful to fishery managers as an example of an ecosystem-based approach to protected species management that is adaptive and accounts for multiple objectives.

Exame da filosofia de Nietzsche sob o ponto de vista político

O tema da existência ou inexistência de uma filosofia política nietzschiana é recorrente nos meios acadêmicos, e é imensamente problemático desde a vinculação do nome do filósofo às ideologias fascistas da primeira metade do século XX. Especialmente a partir da segunda metade do século XX, a filosofia de Nietzsche tem sido trazida para os debates políticos, dessa vez como uma filosofia das grandes causas, daqueles que buscam a libertação do jugo dos grandes esquemas políticos da modernidade. O objetivo inicial desta dissertação é demonstrar que filosofia de Nietzsche não possui as características que permitam a sua assimilação pelo debate político. O próprio filósofo, reiteradamente, negou-se a ingressar no debate político de seu tempo, recusando-se a limitar seu exame da filosofia e suas reflexões às necessidades e clamores da plebe. Ele alertou para a dureza e radicalidade de seu pensamento, antecipando a vinculação de seu nome a coisas terríveis. Em vista disso, pretende-se levar a cabo nesta dissertação um exame da filosofia nietzschiana sob o ponto de vista da política, isto é, tentar ver se ao quadro geral da filosofia política pode-se juntar o pensamento de Nietzsche. Este exame deve ser feito levando-se em conta o amplo auditório ao qual se destinam os discursos políticos, o vínculo dos discursos políticos aos clamores da plebe, ou ao discurso de dominação. O objetivo final desta dissertação será demonstrar que fora do âmbito da filosofia, isto é, trazida para o seio do senso comum, a filosofia de Nietzsche, dado o caráter controvertido de suas asserções, acaba sendo presa fácil, mais uma vez, dos discursos de dominação e servindo aos piores propósitos. Corre-se o risco, outra vez, de se confirmar o vaticínio do filósofo quanto a sua vinculação a coisas terríveis.

The Fisheries for Mangrove Cockles,Anadaraspp., from Mexico to Peru, With Descriptions of Their Habitats and Biology, the Fishermen’s Lives, and the Effects of Shrimp Farming

This paper provides the first description of the mangrove cockle, Anadara spp., fisheries throughout their Latin American range along the Pacific coast from Mexico to Peru. Two species, A. tuberculosa and A. grandis, are found over the entire range, while A. similis occurs from El Salvador to Peru. Anadara tuberculosa is by far the most abundant, while A. grandis has declined in abundance during recent decades. Anadara tuberculosa and A. similis occur in level mud sediments in mangrove swamps, comprised mostly of Rhizophora mangle, which line the main-lands and islands of lagoons, whereas A. grandis inhabits intertidal mud flats along the edges of the same mangrove swamps. All harvested cockles are sexually mature. Gametogenesis of the three species occurs year round, and juvenile cockles grow rap-idly. Cockle densities at sizes at least 16–42 mm long ranged from 7 to 24/m2 in Mexico. Macrofaunal associates of cockles include crustaceans, gastropods, and finfishes. The mangrove swamps are in nearly pristine condition in every country except Honduras, Ecuador, and Peru, where shrimp farms constructed in the 1980’s and 1990’s have destroyed some mangrove zones. In addition, Hurricane Mitch destroyed some Honduran mangrove swamps in 1998. About 15,000 fishermen, including men, women, and children, harvest the cockles. Ecuador has the largest tabulated number of fishermen, 5,055, while Peru has the fewest, 75. Colombia has a large number, perhaps exceeding that in Ecuador, but a detailed census of them has never been made. The fishermen are poor and live a meager existence; they do not earn sufficient money to purchase adequate food to allow their full health and growth potential. They travel almost daily from their villages to the harvesting areas in wooden canoes and fiberglass boats at low tide when they can walk into the mangrove swamps to harvest cockles for about 4 h. Harvest rates, which vary among countries owing to differences in cockle abundances, range from about 50 cockles/fisherman/day in El Salvador and Honduras to 500–1,000/ fisherman/day in Mexico. The fishermen return to their villages and sell the cockles to dealers, who sell them mainly whole to market outlets within their countries, but there is some exporting to adjacent countries. An important food in most countries, the cockles are eaten in seviche, raw on the half-shell, and cooked with rice. The cockles are under heavy harvesting pressure, except in Mexico, but stocks are not yet being depleted because they are harvested at sizes which have already spawned. Also some spawning stocks lie within dense mangrove stands which the fishermen cannot reach. Consumers fortunately desire the largest cockles, spurning the smallest. Cockles are important to the people, and efforts to reduce the harvests to prevent overfishing would lead to severe economic suffering in the fishing communities. Pro-grams to conserve and improve cockle habitats may be the most judicious actions to take. Preserving the mangrove swamps intact, increasing their sizes where possible, and controlling cockle predators would lead to an increase in cockle abundance and harvests. Fishes that prey on juvenile cockles might be seined along the edges of swamps before the tide rises and they swim into the swamps to feed. Transplanting mangrove seedlings to suitable areas might increase the size of those habitats. The numbers of fishermen may increase in the future, because most adults now have several children. If new fishermen are tempted to harvest small, immature cockles and stocks are not increased, minimum size rules for harvestable cockles could be implemented and enforced to ensure adequate spawning.