The relationship between boat size and fish catches in the gillnet fishery of Lake Victoria, Uganda

The number and size composition of gillnets, fishing grounds, and the quantity and composition of fish catches were related to the size of fishing boat. The overall number of gillnets per boat increased from 20.9 + or - 2.3 nets in 5-6 m long boats to 88.6 + or - 11.8 nets in 11-12 m long boats. The proportion of large mesh sizes, + or more than 127 mm, also increased from 40% in 5-6 m long boats to 100% in boats longer than 10 m. Fish catches are related to the size of boat and this should be considered when formulating management guidelines of the lake's fishery. Promotion of large fishing boats 8 m or longer and restriction on the number and/or mesh size of gillnets of smaller boats could increase ecological and socio-economic benefits.

Effects of the 1997-1998 El Niño on population size and diet of the Galápagos sea lion (Zalophus wollebaeki)

The multi-annual climatic event, El Niño Southern Oscillation (ENSO) is an important factor in the population dynamics of coastal marine species in the Galápagos. The Galápagos sea lion, Zalophus wollebaeki, suffered an apparent population decline of about 50%, considering both mortality and movements away from study sites during the 1997-98 El Niño. This change was in part due to changes in the availability of sardines of the Family Clupeidae, its main prey. These declines resulted partly from elevated mortality (35%) in sea lion colonies, particularly among pups, juveniles (< 1 year old), and dominant males and as a result of movements of adults elsewhere (15%), presumably where there were alternative prey and better environmental conditions.

Reconstruction of original body size and estimation of allometric relationships for the longfin inshore squid (Loligo pealeii) and northern shortfin squid (Illex illecebrosus)

Quantification of predator-prey body size relationships is essential to understanding trophic dynamics in marine ecosystems. Prey lengths recovered from predator stomachs help determine the sizes of prey most influential in supporting predator growth and to ascertain size-specific effects of natural mortality on prey populations (Bax, 1998; Claessen et al., 2002). Estimating prey size from stomach content analyses is often hindered because of the degradation of tissue and bone by digestion. Furthermore, reconstruction of original prey size from digested remains requires species-specific reference materials and techniques. A number of diagnostic guides for freshwater (Hansel et al., 1988) and marine (Watt et al., 1997; Granadeiro and Silva, 2000) prey species exist; however they are limited to specific geographic regions (Smale et al., 1995; Gosztonyi et al., 2007). Predictive equations for reconstructing original prey size from diagnostic bones in marine fishes have been developed in several studies of piscivorous fishes of the Northwest Atlantic Ocean (Scharf et al., 1998; Wood, 2005). Conversely, morphometric relationships for cephalopods in this region are scarce despite their importance to a wide range of predators, such as finfish (Bowman et al., 2000 ; Staudinger, 2006), elasmobranchs (Kohler, 1987), and marine mammals (Gannon et al., 1997; Williams, 1999).

A 4500-year time series of Pacific cod (Gadus macrocephalus) size and abundance: archaeology, oceanic regime shifts, and sustainable fisheries

A 4500-year archaeological record of Pacific cod (Gadus macrocephalus) bones from Sanak Island, Alaska, was used to assess the sustainability of the modern fishery and the effects of this fishery on the size of fish caught. Allometric reconstructions of Pacific cod length for eight prehistoric time periods indicated that the current size of the nearshore, commercially fished Pacific cod stocks is statistically unchanged from that of fish caught during 4500 years of subsistence harvesting. This finding indicates that the current Pacific cod fishery that uses selective harvesting technolog ies is a sustainable commercial fishery. Variation in relative Pacific cod abundances provides further insights into the response of this species to punctuated changes in ocean climate (regime shifts) and indicates that Pacific cod stocks can recover from major environmental perturbations. Such palaeofisheries data can extend the short time-series of fisheries data (<50 yr) that form the basis for fisheries management in the Gulf of Alaska and place current trends within the context of centennial- or millennial-scale patterns.

Distribution of red deepsea crab (Chaceon quinquedens) by size and sex in the Gulf of Mexico

The red deepsea crab (Chaceon quinquedens (Smith, 1879)) has supported a commercial fishery off the coast of New England since the 1970s (Wigley et al., 1975) and has had annual harvests from 400 metric tons (t) (1996) to 4000 t (2001) (NEFMC, 2002). In 2002, a fishery management plan for the northeast fishery on the Atlantic coast was implemented and total allowable catch was reduced to approximately 2500 t (NEFMC, 2002). Although there are management plans for the golden crab (C. fenneri) and the red deep sea crab for Atlantic coast regions, there is no fishery management plan for red deepsea crabs in the Gulf of Mexico. Successful management for sustainable harvests should be based on a knowledge of the life history of the species, but C. quinquedens has been a difficult species for which to obtain life history and abundance information because of its deep distribution.

The role of mate guarding, Male Size and Male Investment on Individual Reproductive Success in the Blue Crab, Callinectes Sapidus.

Male blue crabs, Callinectes Sapidus, guard their mates before and after mating, suggesting that the conditions regulating both types of mate guarding dictate individual reproductive success. I tested the hypothesis that large male blue crabs have advantages in sexual competition using experimental manipulations, a simulation model, and field data on crabs from mid-Chesapeake Bay between 1991-1994.

Review of size- and age-dependence in batch spawning: implications for stock assessment of fish species exhibiting indeterminate fecundity

Most assessments of fish stocks use some measure of the reproductive potential of a population, such as spawning biomass. However, the correlation between spawning biomass and reproductive potential is not always strong, and it likely is weakest in the tropics and subtropics, where species tend to exhibit indeterminate fecundity and release eggs in batches over a protracted spawning season. In such cases, computing annual reproductive output requires estimates of batch fecundity and the annual number of batches—the latter subject to spawning frequency and duration of spawning season. Batch fecundity is commonly measured by age (or size), but these other variables are not. Without the relevant data, the annual number of batches is assumed to be invariant across age. We reviewed the literature and found that this default assumption lacks empirical support because both spawning duration and spawning frequency generally increase with age or size. We demonstrate effects of this assumption on measures of reproductive value and spawning potential ratio, a metric commonly used to gauge stock status. Model applications showed substantial sensitivity to age dependence in the annual number of batches. If the annual number of batches increases with age but is incorrectly assumed to be constant, stock assessment models would tend to overestimate the biological reference points used for setting harvest rates. This study underscores the need to better understand the age- or size-dependent contrast in the annual number of batches, and we conclude that, for species without evidence to support invariance, the default assumption should be replaced with one that accounts for age- or size-dependence.

A comparison of size and age of red snapper (Lutjanus campechanus) with the age of artificial reefs in the northern Gulf of Mexico

Despite extensive study, it still is not clear whether artificial reefs produce new fish biomass or whether they only attract various species and make them more vulnerable to fishing mortality. To further evaluate this question, the size and age of red snapper (Lutjanus campechanus) were sampled from April to November 2010 at artificial reefs south of Mobile Bay off the coast of Alabama and compared with the age of the artificial reef at the site of capture. Red snapper were collected with hook and line and a fish trap and visually counted during scuba-diver surveys. In the laboratory, all captured red snapper were weighed and measured, and the otoliths were removed for aging. The mean age of red snapper differed significantly across reefs of different ages, with older reefs having older fish. The mean age of red snapper at a particular reef was not related to reef depth or distance to other reefs. The positive correlation between the mean age of red snapper and the age of the reef where they were found supports the contention that artificial reefs in the northern Gulf of Mexico enhance production of red snapper. The presence of fish older than the reef indicates that red snapper are also attracted to artificial reefs.