Natural mortality rate, annual fecundity, and maturity at length for Greenland halibut (Reinhardtius hippoglossoides) from the northeastern Pacific Ocean

Mortality, fecundity, and size at maturity are important life history traits, and their interactions determine the evolution of life history strategies (Roff, 1992; Stearns, 1992; Charnov, 2002). These same traits are also important for population dynamics models (Hunter et al., 1992; Clark, 1999). It is increasingly important to accurately determine Greenland halibut (Reinhardtius hippoglossoides) life history traits and to correctly assess the status of its stocks because low recruitment or low biomass estimates have led to catch restrictions in the Bering Sea and Aleutian Islands (Ianelli et al.1), the Northeastern Arctic (Ådlandsvik et al., 2004), and the Northwest Atlantic (Bowering and Nedreaas, 2000).

Precision estimates and suggested sample sizes for length-frequency data

For most fisheries applications, the shape of a length-frequency distribution is much more important than its mean length or variance. This makes it difficult to evaluate at which point a sample size is adequate. By estimating the coefficient of variation of the counts in each length class and taking a weighted mean of these, a measure of precision was obtained that takes the precision in all length classes into account. The precision estimates were closely associated with the ratio of the sample size to the number of size classes in each sample. As a rule-of-thumb, a minimum sample size of 10 times the number of length classes in the sample is suggested because the precision deteriorates rapidly for smaller sample sizes. In absence of such a rule-of-thumb, samplers have previously under-estimated the required sample size for samples with large fish, while over-sampling small fish of the same species.

Precision and accuracy of fish length measurements obtained with two visual underwater methods

During the VITAL cruise in the Bay of Biscay in summer 2002, two devices for measuring the length of swimming fish were tested: 1) a mechanical crown that emitted a pair of parallel laser beams and that was mounted on the main camera and 2) an underwater auto-focus video camera. The precision and accuracy of these devices were compared and the various sources of measurement errors were estimated by repeatedly measuring fixed and mobile objects and live fish. It was found that fish mobility is the main source of error for these devices because they require that the objects to be measured are perpendicular to the field of vision. The best performance was obtained with the laser method where a video-replay of laser spots (projected on fish bodies) carrying real-time size information was used. The auto-focus system performed poorly because of a delay in obtaining focus and because of some technical problems.

Variation in trawl geometry due to unequal warp length

Survey standardization procedures can reduce the variability in trawl catch efficiency thus producing more precise estimates of biomass. One such procedure, towing with equal amounts of trawl warp on both sides of the net, was experimentally investigated for its importance in determining optimal trawl geometry and for evaluating the effectiveness of the recent National Oceanic and Atmospheric Administration (NOAA) national protocol on accurate measurement of trawl warps. This recent standard for measuring warp length requires that the difference between warp lengths can be no more than 4% of the distance between the otter doors measured along the bridles and footrope. Trawl performance data from repetitive towing with warp differentials of 0, 3, 5, 7, 9, 11, and 20 m were analyzed for their effect on three determinants of flatfish catch efficiency: footrope distance off-bottom, bridle length in contact with the bottom, and area swept by the net. Our results indicated that the distortion of the trawl caused by asymmetry in trawl warp length could have a negative inf luence on flatfish catch efficiency. At a difference of 7 m in warp length, the NOAA 4% threshold value for the 83112 Eastern survey trawl used in our study, we found no effect on the acous-tic-based measures of door spread, wing spread, and headrope height off-bottom. However, the sensitivity of the trawl to 7 m of warp offset could be seen as footrope distances off-bottom increased slightly (particularly in the center region of the net where flatfish escapement is highest), and as the width of the bridle path responsible for flatfish herding, together with the effective net width, was reduced. For this survey trawl, a NOAA threshold value of 4% should be considered a maximum. A more conservative value (less than 4%) would likely reduce potential bias in estimates of relative abundance caused by large differences in warp length approaching 7 m.

Length-weight relationship of fishes caught by trawl off Alexandria, Egypt

This paper presents the length-weight relationship parameters (a and b) for 29 fish species, belonging to 16 families, taken by otter trawl fishing from Egyptian Mediterranean waters. The b values obtained ranged from 2.50 to 3.44 (with a mean of 2.926).

Length-weight relationships of commercially important marine fishes and shellfishes of the southern coast of Karnataka, India

The parameters of the length-weight relationship of the form W = aLb are presented for 51 species of commercially important marine fishes and shellfishes caught along the southern coast of Karnataka, India. Samples from commercial (trawl, purse seines, gill nets) and artisanal gears were taken during August 1999 to May 2001. The ‘b’ value ranged between 1.942 and 3.616 with a mean of 2.80, standard deviation of 0.32, and mode of 3.

Length-weight relationships of major carps in Kaptai Lake, Bangladesh

Length-weight relationships and condition factors are presented for Indian major carp Catla catla, Labeo rohita, L. calbasu and Cirrhinus mrigala (Cyprinidae) in a reservoir of Bangladesh (Kaptai Lake).

Length-weight relationship of fishes from Yemen waters (Gulf of Aden and Red Sea)

The data for this study were gathered between 1993 and 1996 on board commercial trawlers from Somalia, China and Yemen and also from the research vessel Ibn Magid belonging to the Marine Science and Resources Research Centre, Aden, Republic of Yemen. Fish were identified using the FAO species identification literature. All fish were measured to the nearest mm (total length) and weighed to the nearest g. Sex was determined by dissection after the length and weight had been measured. The length-weight relationships were calculated using least-squares regression on log-transformed data and the parameters of the relationship of the form of W=aL super(b) are summarized. Maximum and minimum size of fish sampled are also given. Common names and recent changes in nomenclature were taken from ICLARM's FishBase.

A comparison of length-related and age-related growth parameters of newaiby Otolithes ruber in Kuwait waters

The growth parameters of Otolithes ruber (Sciaenidae) were determined from both length-frequency and length-at-age data collected from Kuwait waters from 1984 to 1986. The similarity of the growth parameters is reflected in the small range of the parameters o' (=log sub(10)K+2logL) which indicates the compatibility of the two methods for this relatively short-lived species.

Length-weight relationship and relative condition of Heterobranchus longifilis (Valenciennes) from Idodo River, Nigeria

Length-weight relationship parameters of Heterobranchus longifilis males, females and combined sexes are given. The samples were collected from Idodo River, with size ranging from 123 mm total length, L, to 936 mm L. The values obtained for the mean L by sex show that males were significantly (p<0.05) larger than females. The results show that the slope (b) is significantly (p<0.05) below 3.0 for the male, female and pooled sample. The species exhibit a negative allometric growth pattern. The relative condition of fish shows seasonal variation, with females generally being in better condition than the males.

Length-weight relationship of fishes caught in the Itaipu Reservoir, Parana, Brazil

Parameters and related statistics of the length-weight relationship of the form W=aL super(b) are presented for 72 species of fish caught in the area of the Itaipu Reservoir in Parana, Brazil. The b values varied between 2.34 and 3.35, with the mean b=2.986 (s.d.=0.230) not significantly different from 3.0 (df=7, p=0.05).

Length-weight relationship of small pelagic fish species of the southeast and South Brazilian Exclusive Economic Zone

The length-weight relationship (LWR) parameters of 23 small pelagic fish species (belonging to 13 families) from the south-southeast Brazilian Exclusive Economic Zone in 1996 and 1997 are presented. The b values varied between 2.72 and 3.53. The samples for this study were collected during hydroacoustic surveys covering an area of 700 000 square km.

A simple spreadsheet model to incorporate seasonal growth into length-based stock assessment methods

The paper describes a method by which seasonal growth can be incorporated into length-converted catch curves and cohort analyses using a spreadsheet. The method is based on calculating the length of fish using seasonal growth parameters on a daily basis. A LOOKUP function is then used to find the age corresponding to the length.