Diets of Steller sea lions (Eumetopias jubatus) in Southeast Alaska, 1993−1999

The diet of Steller sea lions (Eumetopias jubatus) was determined from 1494 scats (feces) collected at breeding (rookeries) and nonbreeding (haulout) sites in Southeast Alaska from 1993 to 1999. The most common prey of 61 species identified were walleye pollock (Theragra chalcogramma), Pacific herring (Clupea pallasii), Pacific sand lance (Ammodytes hexapterus), Pacific salmon (Salmonidae), arrowtooth flounder (Atheresthes stomias), rockfish (Sebastes spp.), skates (Rajidae), and cephalopods (squid and octopus). Steller sea lion diets at the three Southeast Alaska rookeries differed significantly from one another. The sea lions consumed the most diverse range of prey categories during summer, and the least diverse during fall. Diet was more diverse in Southeast Alaska during the 1990s than in any other region of Alaska (Gulf of Alaska and Aleutian Islands). Dietary differences between increasing and declining populations of Steller sea lions in Alaska correlate with rates of population change, and add credence to the view that diet may have played a role in the decline of sea lions in the Gulf of Alaska and Aleutian Islands.

Length-weight relationships of demersal fishes from the Gulf of Salamanca, Colombia: [part 2]

The parameters a and b of the length-weight relationship of the form W=aL super(b) are presented for 37 fish species, belonging to 17 families, caught during a demersal trawl survey over the period December 1995 to March 1998 in the Gulf of Salamanca, Colombia

Length-weight relationships of freshwater fishes in Greece

Length-weight relationships were calculated for nine fish species from Lake Volvi (Macedonia, Hellas), caught with gillnets of five different mesh sizes between October 1995 and October 1996. In addition, length-weight relationships for 24 Greek freshwater fish species and one hybrid were also obtained from the literature. The values of the exponent of the length-weight relationships for all fish species examined ranged between 2.14 and 3.70 (mean = 3.12; SE=0.0321), and the median value was 3.19.

Beverton and Holt equations: spreadsheet functions and uncertainty

This contribution illustrates how modern spreadsheets aid the calculation and visualization of yield models and how the effects of uncertainties may be incorporated using Monte Carlo simulation. It is argued that analogous approaches can be implemented for other assessment models of simple to medium complexity justifying wider use of spreadsheets in fisheries analysis and training.

Preliminary observation on culture of Penaeus monodon in low-saline waters

The feasibility of semi-intensive culture of Penaeus monodon in low saline environment was investigated by comparing the growth and production in low (0.16-6.52 ppt) and high (4.60-19.42 ppt) saline areas at two stocking densities (10.5 and 16 individuals/m super(2)). After 135 days of culture, yield of shrimp in low and high stocking densities was 1563.37 kg/ha and 2274 kg/ha, respectively, in low saline ponds, and 1173.00 and 1974.00 kg/ha, respectively in high saline ponds. Food conversion ratio (FCR, 1.31-1.58) and specific growth rate (SGR 21.04-21.19%) were higher in low saline ponds as compared to high saline ponds (FCR, 1.35-1.68; SGR, 19.22-19.88%). Growth of shrimp was satisfactory in low saline ponds even when salinity decreased after 60 days of culture to almost freshwater level (0.16 ppt) indicating the variability of semi-intensive culture of P. monodon in low saline environment.

Abundance and distribution of California sea lions (Zalophus californianus) in central and northern California during 1998 and summer 1999

The abundance and distribution of California sea lions (Zalophus californianus) in central and northern California was studied to allow future evaluation of their impact on salmonids, the ecosystem, and f isheries. Abundance at-sea was estimated by using the strip transect method from a fixed-wing aircraft with a belly viewing port. Abundance on land was estimated from 126-mm-format aerial photographs of animals at haulouts between Point Conception and the California−Oregon border. The sum of these two estimates represented total abundance for central and northern California. Both types of survey were conducted in May−June 1998, September 1998, December 1998, and July 1999. A haulout survey was conducted in July 1998. The greatest number of sea lions occurred near Monterey Bay and San Francisco Bay for all surveys. Abundance was high in central and northern California in 1998 when warm water from the 1997−98 El Niño affected the region and was low in July 1999 when cold water La Niña conditions were prevalent. At-sea abundance estimates in central and northern California ranged from 12,232 to 40,161 animals, and haulout abundance was 13,559 to 36,576 animals. Total abundance of California sea lions in central and northern California was estimated as 64,916 in May−June 1998, 75,673 in September 1998, 56,775 in December 1998, and 25,791 in July 1999. The proportion of total abundance to animals hauled-out for the four complete surveys ranged from 1.77 to 2.13, and the mean of 1.89 was used to estimate a total abundance of 49,697 for July 1998. This multiplier may be applicable in the future to estimate total abundance of California sea lions off central and northern California if only the abundance of animals at haulout sites is known.

Abundance of Belugas, Delphinapterus leucas, in Cook Inlet, Alaska, 1994–2000

Annual abundance estimates of belugas, Delphinapterus leucas, in Cook Inlet were calculated from counts made by aerial observers and aerial video recordings. Whale group-size estimates were corrected for subsurface whales (availability bias) and whales that were at the surface but were missed (detection bias). Logistic regression was used to estimate the probability that entire groups were missed during the systematic surveys, and the results were used to calculate a correction to account for the whales in these missed groups (1.015, CV = 0.03 in 1994–98; 1.021, CV = 0.01 in 1999– 2000). Calculated abundances were 653 (CV = 0.43) in 1994, 491 (CV = 0.44) in 1995, 594 (CV = 0.28) in 1996, 440 (CV = 0.14) in 1997, 347 (CV = 0.29) in 1998, 367 (CV = 0.14) in 1999, and 435 (CV = 0.23, 95% CI=279–679) in 2000. For management purposes the current Nbest = 435 and Nmin = 360. These estimates replace preliminary estimates of 749 for 1994 and 357 for 1999. Monte Carlo simulations indicate a 47% probability that from June 1994 to June 1998 abundance of the Cook Inlet stock of belugas was depleted by 50%. The decline appears to have stopped in 1998.

An Index of Abundance for Coastal Species of Juvenile Sharks from the Northeast Gulf of Mexico

A fishery-independent assessment of juvenile coastal shark populations in U.S. waters of the northeast Gulf of Mexico was conducted using two methods: gillnets and longlines. Surveys were conducted monthly during April–October in two fixed sampling areas from 1996 to 1998. The Atlantic sharpnose shark, Rhizoprionodon terraenovae, and the blacktip shark, Carcharhinus limbatus, were the most common species captured with either longlines or gillnets. An additional 14 shark species were captured, and juvenile indices of abundance were developed for 8 species with gillnets and 6 species of sharks with longlines. Trends in catch-per-unit-effort were found to vary depending on species. Length-frequency information revealed that the majority of sharks captured were juveniles. Given the direct relationship between stock and recruitment for sharks, continued monitoring of juvenile abundance will aid in determining the strength of the parental stock size and for predicting future population strength.

Front pages with contents of No. 37, 1983

Contents.

Additional crayfish survey of Checkley Brook, Hollywood End Brook and Black Brook (Goyt) 1999

This is the report on the Additonal Crayfish Survey of Checkley Brook, Hollywood End Brook and Black Brook from 1999 by the Environment agency. The aim of the 1999 survey was to obtain a more complete picture of the crayfish distribution in those areas. It contains sections on the sampling methodology which followed the sampling done in 1998, the results of the sampling indicating the species of crayfish occurring in the sampling areas and some discussion and conclusions for each area. The appendix I contains maps locating the sampling points and past records. The appendix II contains detailed information of the sampling points.

Gunnislake Fish Counter. Annual Report 1999

This is the Gunnislake Fish Counter, Annual Report 1999 produced by the Environment Agency South West Region on March 2000. The report presents the daily upstream counts of migratory salmonids recorded at Gunnislake Weir fish counting station (SX 435 713) situated on the River Tamar in 1999. The counter data contained within this report covers the period of the commercial migratory salmonid net buy-back scheme and the implementation of the National Spring Salmon Byelaws. The fish counter at Gunnislake is a resistivity based system (Logie 2100A – Aquantic limited) and is installed in the fish pass on the Cornish bank of the River Tamar at the head of the tide. The minimum salmon count for 1999 was 2691. The run pattern observed for salmon and sea trout in 1999 was generally consistent with that of previous years. However, the total combined annual count of salmon and sea trout migrating upstream on the River Tamar in 1999 was 25% higher than the 5 year average (1994 - 1998).

Restormel Fish Counter Annual Report 1999

This is the Restormel Fish Counter, Annual Report 1999 produced by the Environment Agency South West Region on March 2000. The report presents the daily upstream counts of migratory salmonids recorded at Restormel Weir counting station (SX 107 613) River Fowey in 1999. The counter data covers the period of the commercial migratory salmonid net buy-back scheme, which was in operation between March and June 1999. The fish counter is a resistivity based system (Logie 2100 A - Aquantic limited) and operates over all three channels of the weir at Restormel. The minimum salmon count estimate was 497, and the 1999 upstream count for sea trout was 6590. The run pattern observed for salmon and sea trout in 1999 was generally consistent with that of previous years. Flows on average were half those of 1998 during September, October, and November.