A century of fishery data documenting the collapse of smooth‐hounds (Mustelus spp.) in the Mediterranean Sea

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Use of parasites as biological tags for separating stocks of the starspotted dogfish Mustelus manazo in Japan and Taiwan

ABSTRACT:   The parasite fauna of Mustelus manazo from seven localitiesin Japan and Taiwan was assessed for the feasibility of using parasitesas biological tags for the identification of different host stocks.Examination of 1038 host specimens resulted in 13 parasite speciesrecorded: one nematode, two myxosporeans, two copepods and eightcestodes. Although relatively low overall prevalence of the firstfive species at different localities showed some significant differences,the samples collected in Tokyo Bay bore the lowest similarity (19.2%).These results support previous studies, which suggested the existenceof a unique host stock in Tokyo Bay. Accordingly, combinations ofprevalence data may provide useful information on stock identification.Cestodes probably have the greatest potential for use as biologicaltags. Detailed examination of 25 specimens of M .  manazo fromAomori and Tokyo Bay disclosed eight species of intestinal cestodes.A canonical discriminant analysis based on these species separatedthe two localities clearly.     

Genetic variation between populations of starspotted dogfish Mustelus manazo in central Japan and northern Taiwan

SUMMARY: The genetic structure of the samples of Mustelus manazo between central Japan and Taiwan was investigated by starch gel electrophoresis. From a total of 20 enzyme loci scored, only two of them ( CK-A and sSOD-1 ) showed polymorphism with sufficient allelic variation that would be useful for analysis of population structure. The Taiwanese samples have unique allele of CK-A 52 and sSOD-1 40 that are absent in the Japanese samples. Mean heterozygosity values were 0.027 and 0.055 for two Taiwanese samples and 0.008 and 0.013 for two Japanese samples. The chi-square analysis shows significant differences ( P < 0.001) between the pooled central Japanese samples and Taiwanese samples indicating that they are two separate populations with moderate divergence ( F_ST = 0.063). A possible explanation of population divergence between the two countries is also discussed.     

The food habits of four species of triakid sharks, Triakis scyllium, Hemitriakis japanica, Mustelus griseus and Mustelus manazo, in the central Seto Inland Sea, Japan

ABSTRACT:   The food habits of 595 houndsharks of four species, Triakis scyllium ( n  = 179, 42–148 cm total in length), Hemitriakis japanica ( n  = 57, 42–102 cm), Mustelus griseus ( n  = 193, 39–100 cm), and Mustelus manazo ( n  = 166, 43–120 cm), found in the central Seto Inland Sea, Japan, from March 1997 to October 1999 and May 2000 to July 2002, were studied. T. scyllium changed their main food items from shrimps to echiuran worms then to cephalopods with their growth. Comparing food habits by the value of similarity (maximum = 1), the small-sized T. scyllium had a low value (0.17) compared to larger sharks. T. scyllium gradually increased the diversity of food until it reached 700 mm long in total length, however, after that it decreased. H. japanica appeared mainly in summer and autumn and ate cephalopods and fishes. M. griseus preyed on various crustaceans and decreased the diversity of food with growth. M. manazo preferred crustaceans and polychaetes. There was no certain tendency in the diversity of the food habit for M. manazo .     

Food variations and ontogenetic dietary shift of the starspotted-dogfish Mustelus manazo at five locations in Japan and Taiwan

SUMMARY: Stomach contents were examined from 936 individuals of Mustelus manazo , collected by trawl at five locations: Aomori, Tokyo Bay, Maizuru and Shimonoseki in Japan, and one location off Taiwan. The vacuity index was relatively low (0–6.1%). Based on three indices ( %W , %F , RI ), the major dietary component was crustaceans at all locations. The most important prey category was crabs in Aomori, Shimonosei and Taiwan, mantis shrimps in Tokyo Bay, and shrimps in Maizuru. Fishes were a minor food category for M. manazo in most locations, except in Maizuru where fishes were second in importance in the diet. Dietary overlap revealed a medium degree of overlap between Tokyo Bay and Aomori, and between Tokyo Bay and Shimonoseki. The other locations showed a high degree of overlap with each other. Significant ontogenetic dietary shifts were found in Tokyo Bay, Maizuru and Taiwan, and prey diversity showed a trend being relatively low in larger size classes. The feeding habit of M. manazo was unique in Tokyo Bay, where crustaceans in the muddy substrata were taken in preference to the most abundant benthic prey item available, such as a southern rough shrimp, Trachypenaeus curvirostris . Mustelus manazo appears to use two feeding strategies based upon stomach contents. One, in Tokyo Bay, involved the digging up or removing of burrowing invertebrates from muddy substrata without crushing them. The other, at the other four locations, involved the crushing of prey on the substrata surface.