Dolphin caught by charter boats fishing over the Continental Shelf in 1961-63 were examined to determine food habits and sex ratios. Most important prey (listed according to percent of total prey weight) were: Exocoetidae (26%), Scombridae (22%), Carangidae(12%), Balistidae (9%), and Coryphaenidae (5%). Males constituted a significant majority (61%) of large dophin (801-1,275 mm fork length). Most (71%) small dolphin (450400 mm) were females. Large dolphin of both sexes were generally captured in open water, while small female dolphin were usually associated with fidedines (areas where current patterns cause accumulations of floating Sargassum and other flotsam). In 1963, tidedines were infrequently encountered by charter boats. Decreased charter boat catches, increased abundance of young males in the fishery, and impaired foraging by small female dolphin resulted. We hypothesize that male dolphin (which are heavier than females of similar length) leave the sanctuary of the tidedine at an earlier age than females to forage for large prey in the open ocean. Thus, most small dolphin captured near tide-lines and associated flotsam are females. Most large dolphin captured by trolling are males, because their significantly greater weight per unit of length results in more voracious feeding and increased selection by the charter boat fishery.
The validity of age determinations from scales of dolphin (Coryphaena hippurus) captured off the North Carolina coast is established. Specimens were obtained from the local charter boat fishery. The greatest age of dolphin examined was 3 years. None of the 3‐year‐old fish and few of the 2‐year‐old fish were females. Predominance of males in age‐groups II and III is believed to be caused by differential feeding habits of the sexes. Analysis of stomach contents indicates that older males may be more voracious feeders than older females; and, therefore, are more susceptible to capture by the hook‐and‐line fishery.
Males are heavier than females throughout their complete length range. The body‐scale relation is efficiently described by linear regression. Theoretical fish length at the time of scale formation was 93.75 mm. Growth in length of male and female dolphin was not significantly different. Rate of growth was independent of year of collection. Length at time of first annular formation was 653 mm. Annual increments were 271 mm during the 2nd year, and 263 mm during the 3rd year.
Comparisons were made of the performance of the 10-d freshwater sediment toxicity tests using the amphipod Hya-leNa azteca and midge Chironornus tentans. Sediments were collected from eight stations in Onondaga Lake, New York, and represented a wide range of toxicity. The biological end points were survival, biomass, and body length. The two tests were compared on the basis of correspondence among relative values of the end points and ability to statistically discriminate adverse effects relative to control responses (Le., discriminatory ability). Minimum detectable differences (MDDs) and adverse response ranges of the end points were used to further evaluate the discriminatory ability of the end points. Relative responses and discriminatory abilities of the end points of both tests were similar, despite numerous differences that exist among characteristics of the test species and end points. Significant concordance was found among all end points with respect to relative toxicity of sediments from the eight stations. Although MDDs and adverse response ranges of the various end points differed substantially, the observed positive correlation between those two variables resulted in all end points having similar discriminatory ability, Although amphipod biomass and body length have rarely been used as end points in 10-d tests, both end points provided results comparable to those of the other end points evaluated in the present study.
Keywords -Freshwater sedimentsSediment toxicity Hyalella azteca Chironornus tentans 2089 * = p 5 0.05; NS = p > 0.05.
Wild and hatchery‐produced shrimp were stocked in two impoundments off Bayou Jean Lacroix in 1968 and 1969. Maximum annual harvest was 141.2 kg/hectare of wild shrimp averaging 119 mm in total length (73 count per kg, heads on) from an impoundment in which attempts were made to remove predators and competitors. Harvest in an impoundment in which predators and competitors were not removed was 48.2, 79.1, and 161.9 kg/hectare of wild shrimp, blue crabs, and large fishes, respectively. Lack of predator control resulted in about a four‐fold decrease in survival of marked white shrimp (Penaeus setiferus). Daily growth rates of juvenile and subadult brown shrimp (P. aztecus) ranged from 1.3 to 1.9 mm and 0.27 to 0.5 mm, respectively, during the investigation. Brown shrimp remaining in an impoundment for the entire 200‐day annual growing season attained 164 mm. Subadult white and pink (P. duorarum) shrimp grew at rates of 0.48 and 0.18 mm/day, respectively. A marking‐recapture study indicated that 70% of subadult brown shrimp were captured during 5 nights of harvesting at an impoundment weir in June, while only 53% of subadult white shrimp were recovered during 22 nights in November. Peak egress of subadult and adult brown shrimp during spring and summer occurred during full and new moons. An apparently causal relationship between decreasing water temperature and white shrimp egress was observed. White shrimp did not survive impoundment life during the winter of 1968‐69.
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