. California fish and game. Fisheries -- California; Game and game-birds -- California; Fishes -- California; Animal Population Groups; Pêches; Gibier; Poissons. 52 CALIFORNIA FISH AND GAME V o 9 o o E 3 Z n n. 25 35 40 45 ToTol Body Length cms. 50 55 60 FIGURE 3. Size frequency distribution of the males and females of Hydrolagus collei. SHADED BARS = MALES DISCUSSION AND CONCLUSIONS Ratfish show a distinct migratory movement, being more abundant and more widespread in the northern Gulf of California in February- March, than in June-September. They do not appear to reproduce dur- ing the perio
. California fish and game. Fisheries -- California; Game and game-birds -- California; Fishes -- California; Animal Population Groups; Pêches; Gibier; Poissons. 52 CALIFORNIA FISH AND GAME V o 9 o o E 3 Z n n. 25 35 40 45 ToTol Body Length cms. 50 55 60 FIGURE 3. Size frequency distribution of the males and females of Hydrolagus collei. SHADED BARS = MALES DISCUSSION AND CONCLUSIONS Ratfish show a distinct migratory movement, being more abundant and more widespread in the northern Gulf of California in February- March, than in June-September. They do not appear to reproduce dur- ing the period of peak abundance, but this requires further investiga- tion. Females predominate in the catch and this could be because of greater vulnerability to the net, as females are on the average larger, but could also be due to females migrating more readily, or even to a natural difference in sex ratio. However, the pattern of an increasing proportion of females in larger fish is a very widespread one and on close investigation is usually found to be accompanied by increasing mortality selective against males. There is no good reason to believe this process does not operate on the Gulf of California population of ratfish. The cause of the migratory movements of ratfish is unknown, but most of the fish species in the northern Gulf of California are more abundant in early spring, so a casual agent with a rather generalized action should be looked for; quite possibly temperature, oxygen con- centration and currents are of great importance. A different mesh size was used in spring 1972 ( cm) and June 1971 ( cm), so the ratfish caught were subject to different net vul- nerabilities at different sampling periods. However, there is no reason to believe that the marked seasonal differences in distribution are caused by biased sampling arising from the different equipment used,. Please note that these images are extracted from scanned page images that may have been digitally enhanced
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