Reassessment of spiny dogfish Squalus acanthias age and growth using vertebrae and dorsal-fin spines.

Male and female spiny dogfish Squalus acanthias were collected in the western North Atlantic Ocean in the Gulf of Maine between July 2006 and June 2009. Squalus acanthias ranged from 25 to 102 cm stretch total length and were caught during all months of the year except January. Age estimates derived from banding patterns visible in both the vertebrae and second dorsal-fin spines were compared. Vertebral growth increments were visualized using a modified histological staining technique, which was verified as appropriate for obtaining age estimates. Marginal increment analysis of vertebrae verified the increment periodicity, suggesting annual band deposition. Based on increased precision and accuracy of age estimates, as well as more biologically realistic parameters generated in growth models, the current study found that vertebrae provided a more reliable and accurate means of estimating age in S. acanthias than the second dorsal-fin spine. Age estimates obtained from vertebrae ranged from <1 year-old to 17 years for male and 24 years for female S. acanthias. The two-parameter von Bertalanffy growth model fit to vertebrae-derived age estimates produced parameters of L∞ = 94·23 cm and k = 0·11 for males and L∞ = 100·76 cm and k = 0·12 for females. While these growth parameters differed from those previously reported for S. acanthias in the western North Atlantic Ocean, the causes of such differences were beyond the scope of the current study and remain to be determined.

The reproductive cycle of the roundel skate Raja texana.

The reproductive cycle of Raja texana was determined from 63 females (510-630 mm total length, L(T)) and 81 males (355-546 mm L(T)) collected from the Gulf of Mexico. The results, based on follicle size, mature spermatocysts and gonadosomatic index (I(G)) suggests year-round reproductive activity.

Age and size at sexual maturity of the smooth skate Malacoraja senta from the western Gulf of Maine.

Age and size at sexual maturity was determined for 185 male and 96 female smooth skates Malacoraja senta (ranging in size from 370 to 680 mm total length L(T)), collected from the western Gulf of Maine. Maturity ogives for males, based on clasper length, testis mass and the proportion of mature spermatocysts in the testes, suggest that 50% maturity occurs between 9 and 10 years and 560 mm L(T). Maturity ogives for females, based on ovary mass, shell-gland mass and maximum follicle size, suggest that 50% maturity occurs at age 9 years and 540 mm L(T).

Size and age estimates at sexual maturity for the little skate Leucoraja erinacea from the western Gulf of Maine, U.S.A.

Size and age estimates at sexual maturity were determined for 162 male and 273 female little skates Leucoraja erinacea collected from the western Gulf of Maine. Maturity ogives suggest that 50% maturity in females occurs at age 9.5 years and 480 mm total length (LT), whereas 50% maturity in males occurs at a slightly younger age of 7.7 years and smaller size of 460 mm LT. Age estimates were made from 389 L. erinacea ranging in size from 93 to 570 mm LT. The index of average per cent error and age-bias plots indicated that the ageing methods were precise and non-biased. Additionally, annual periodicity of band formation was validated with oxytetracycline in eight individuals (three males and five females) ranging in age from 3 to 12 years. In conclusion, results from this study indicate that L. erinacea exhibits characteristics that make other elasmobranch populations highly susceptible to overexploitation.

Effects of environmental dilution on body fluid regulation in the yellow stingray, Urolophus jamaicensis.

Adult yellow stingrays (Urolophus jamaicensis), collected off the southeast Florida coast, were maintained in filtered and re-circulated synthetic sea water (33 per thousand) for 5-13 days at 30 degrees C. Animals exposed to 82%, 74% and 66% SW in gradual steps exhibited rapid and significant weight gains followed by recovery to pre-dilution levels in 2-6 days. Acclimated animals at each salinity [100% (N=12), 82% (7), 74% (4) and 66% SW (3)] were anesthetized (MS222) and bled from the caudal vein. In 100% SW, stingray plasma was slightly hypo-osmotic to the external medium. Plasma osmolality decreased with stepwise dilutions, but became increasingly hyperosmotic to the bathing media. Plasma [Na] and [Cl] each decreased by approximately 13%, 23% and 16%, respectively, in 82%, 74% and 66% SW. Plasma [urea] decreased by 21%, 25% and 59%, respectively. Changes in plasma [K] and [Ca] were minor. Mean corpuscular [Hb] measurements suggest that stingray red cells swelled less at each dilution than predicted for a passive erythrocyte osmometer. RBC [K] decreased by 12%, 36% and 29%, respectively, in 82%, 74% and 66% SW. Quantitatively, the other measured electrolytes (Cl, Na and Ca) changed by lesser amounts. Results suggest that for mild and moderate dilutions (82% and 74% SW), yellow stingrays release both ions and urea from intracellular and extracellular compartments. With further dilution (66% SW), the elasmobranchs retain electrolytes at the expense of urea.