Growth and maturity of salmon sharks (Lamna ditropis) in the eastern and western North Pacific, and comments on back-calculation methods

Age and growth estimates for salmon sharks (Lamna ditropis) in the eastern North Pacific were derived from 182 vertebral centra collected from sharks ranging in length from 62.2 to 213.4 cm pre-caudal length (PCL) and compared to previously published age and growth data for salmon sharks in the western North Pacific. Eastern North Pacific female and male salmon sharks were aged up to 20 and 17 years, respectively. Relative marginal increment (RMI) analysis showed that postnatal rings form annually between January and March. Von Bertalanffy growth parameters derived from vertebral length-at-age data are L∞ =207.4 cm PCL, k=0.17/yr, and t0=−2.3 years for females (n=166), and L∞ =182.8 cm PCL, k=0.23/yr , and t0=−1.9 years for males (n=16). Age at maturity was estimated to range from six to nine years for females (median pre-caudal length of 164.7 cm PCL) and from three to five years old for males (median precaudal length of 124.0 cm PCL). Weight-length relationships for females and males in the eastern North Pacific are W=8.2 × 10_05 × L2.759 –06 × L3.383 (r2 =0.99) and W=3.2 × 10 (r2 =0.99), respectively. Our results show that female and male salmon sharks in the eastern North Pacific possess a faster growth rate, reach sexual maturity earlier, and attain greater weight-at-length than their same-sex counterparts living in the western North Pacific

Hydrodynamic aspects of shark scales

Ridge morphometrices on placoid scales from 12 galeoid shark species were examined in order to evaluate their potential value for frictional drag reduction. The geometry of the shark scales is similar to longitudinal grooved surfaces (riblets) that have been previously shown to give 8 percent skin-friction reduction for turbulent boundary layers. The present study of the shark scales was undertaken to determine if the physical dimensions of the ridges on the shark scales are of the right magnitude to be used by the sharks for drag reduction based on previous riblet work. The results indicate that the ridge heights and spacings are normally maintained between the predicted optimal values proposed for voluntary and burst swimming speeds throughout the individual's ontogeny. Moreover, the species which might be considered to be the faster posses smaller and more closely spaced ridges that based on the riblet work would suggest a greater frictional drag reduction value at the high swimming speeds, as compared to their more sluggish counterparts

Constraints On Sustainable Marine Fisheries In The United States: A Look At The Record

The factors that may constrain or contribute to sustainable marine fisheries were examined by reviewing and analyzing the current state and history of several U.S. fisheries. Among major factors under consideration are: inherent vulnerability, (vulnerability in some species is high because of low intrinsic rates of increase and/or naturally infrequent recruitment); environmental degradation (fisheries may collapse because of anthropogenic habitat destruction); availability of data, (information necessary to conduct accurate stock assessments may not be adequate for some species); quality of the scientific advice, (inappropriate models or scientifically inaccurate assessments may be used); effectiveness of management decisions, (managers may disregard recommendations from scientific committees, and/or implement management measures that are 1 risk prone). Fisheries that are examined include the Atlantic coast striped bass fishery, the New England groundfish fishery, the Atlantic shark fishery, the Atlantic and Gulf reef fish fisheries, and the Pacific rockfish fishery. Although many of the factors listed above contributed to declines in these fisheries, the root cause in all cases was harvesting at rates that were much higher than could be sustained by recruitment. Management was largely ineffective because management decisions were risk prone and motivated by short-term economic considerations rather than long-term sustainability. Only after passage of legislation not only authorizing but specifying mandatory stock rebuilding has most management been sufficiently precautionary to allow sustainability

Characterization of the Demersal Fish Community of a Deep-Sea Radioactive Dump Site (Results of Cruise EPA-7801, R/V ADVANCE II, 21-27 June 1978)

The present report describes the demersal fish fauna collected by otter trawl from RV Advance II on cruise EPA-7801 in the vicinity of a radioactive waste disposal site (R.D.S.) located at a depth of about 3900 m, approximately 200 miles due east of the Virginia coast (Figs. 1, 2). Because the sampling· effort at the R.D.S. was restricted by time and funding, the limited data base accrued from there was analyzed and compared with a much larger data set collected during previous deep-sea trawling studies using the same trawl gear