New microsatellite loci for the endangered scalloped hammerhead shark, Sphyrna lewini

We isolated 15 microsatellite markers for the scalloped hammerhead shark, Sphyrna lewini. Loci were tested on 80 specimens of S. lewini from four Eastern Pacific samples. The number of alleles per locus ranged from 6 to 31 (mean = 14). Observed and expected levels of heterozygosity per locus ranged from 0.39 to 0.91 (mean = 0.70) and from 0.54 to 0.90 (mean = 0.76), respectively. No pairs of loci were in gametic disequilibrium after Bonferroni correction of α. One locus showed significantly lower heterozygosity than expected under Hardy–Weinberg proportions in two populations, possibly caused by null alleles.     

A Cover Story: Fisheries May Drive Stocks to Extinction

The cover of the 1993 reprint of Beverton and Holt's book bears a diagram, its significance previously unrecognized, that expresses extinction due to fishing. This paper traces the concept to self-regenerating yield models in their 1957 book, its numerical development therein far in advance of its reinvention 30 years later. Local extinction constitutes a critical impact of fisheries on aquatic ecosystems that has been too often downplayed by fisheries science.     

Daily egg production ofTemora longicornis (Copepoda,Calanoida) during winter and early spring in the Marsdiep (Southern North Sea)

Mature females of the copepodTemora longicornis from the Marsdiep tidal inlet were incubated at ambient water temperature during the winter of 1989/1990 to estimate their egg production during 24 hours. Throughout winter this production remained at a level of 0 to 10 eggs per female. In March a steep rise to 60 to 80 eggs coincided with an equally steep rise in chlorophyll-a from 4 to 20 g.l^–1. Excess food given during incubation tended to increase the observed production rate only in October at relatively high temperature. Additive effects of rising food level and temperature on daily egg production were found in spring. In March and April 1988 and 1990 the observed maximum daily egg production per female increased from about 20 at 5°C and 5 g.l^–1 chlorophyll to 70 at almost 10°C and 20 g.l^–1. The egg production in winter gives a prebloom potential to maintain a stock of premature stages ready to utilize the algal spring bloom. Early spawning before April can also contribute to the development of the abundance peak of adults in May–June. Due to growth rates increasing with temperature in the months March and April, most of the adults at their peak density may have hatched from eggs before the period of maximum egg production rate at the end of April. The exceptionally high production rate observed at the end of March may be related to a developingPhaeocystis bloom.     

Tidal Influence on Spatial Dynamics of Leopard Sharks, Triakis semifasciata, in Tomales Bay, California

We used ultrasonic telemetry to determine the movement directions and movement rates of leopard sharks, Triakis semifasciata, in Tomales Bay, California. To analyze tide and time of day effects, we surgically implanted transmitters in the peritoneal cavities of one male and five female leopard sharks, which we located during summer for three to five sampling sessions lasting 12 to 24h each. All leopard sharks showed strong movement direction patterns with tide. During incoming tides, sharks moved significantly (p<0.0001) towards the inner bay, apparently to exploit the extensive inner bay muddy littoral zones' food resources. On outgoing tides, sharks showed significant (p<0.0001) movements towards the outer bay. During high tide, there was no discernible pattern to their movements (p=0.092). Shark movement rates were significantly (p<0.0001) greater during dark periods (mean±SE: 10.5±1.0m min^–1), compared with fully lighted ones (6.7±0.5m min^–1). Movement rates of longer sharks tended to be greater than those of shorter ones (range means±SE: 5.8±0.6m min^–1 for the 91cm shark, to 12.8±1.6m min^–1 for the 119cm shark), but the leopard sharks' overall mean movement rate (8.1±0.5m min^–1) was slower than other (more pelagic) sharks.     

Pregnancy in Squaliolus laticaudus (Elasmobranch: Dalatiidae) from Brazil

Synopsis A pregnant female of the Dwarf deep-sea shark, Squaliolus laticaudus with four embryos was caught by the nocturnal longline vessel “Progress?o” from southern Brazil, on September 1999. It was donated by the fishermen. Embryos ranged in size 105 – 100 mm of total length. The aim of this article is to contribute to the knowledge of the Dwarf deep-sea shark reproduction and distribution on the Brazilian coast. It is been considered the first record to know about pregnant Dwarf deep-sea shark in the world.     

Fifty Years On

The traditional approach to providing fisheries management advice through assembly of a population model, estimation of its parameters, identification of optima and calculation of sustainable catch limits is briefly summarised, and its failures noted. An alternative approach, developed first by the Scientific Committee of the International Whaling Commission (IWC) is described. This involves the use of stochastic population models to generate data which are then used in computer simulations of the performances of alternative algorithms for catch limits which do not aim at optima but which satisfy particular sets of management objectives as defined by the management authority.     

Waldfragmentierung, Konkurrenz und klimatische Abh?ngigkeit beim Wespenbussard (Pernis apivorus)

Zusammenfassung Zwischen 1992 und 1997 betrug der Wespenbussard-Bestand eines 110 km² großen, waldarmen Gebietes am nördlichen Alpenrand 7 bis 10 territoriale Paare. Von 10 Waldfragmenten wurden die kleineren signifikant häufiger besetzt. Die Besetzung durch Mäusebussard-Brutpaare beeinflußte die Besetzungsrate von 10 Waldfragmenten nicht signifikant, auch nicht im Zusammenhang mit der Größe der Fragmente. Eine höhere Anzahl von Regentagen im Mai hatte keine Auswirkungen auf die Dichte, und im Juni/Juli bewirkten sie während des Untersuchungszeitraumes keine Einbrüche der Reproduktion. Es wird vorgeschlagen, daß den Faktoren Waldfragmentierung, Konkurrenz und Klima das Nahrungsangebot übergeordnet ist.

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Forest fragmentation, competition and climatic dependence in the Honey Buzzard (Pernis apivorus)

Summary Between 1992 and 1997 a population of Honey Buzzards varied between 7 and 10 territorial pairs on the northern fringe of the Alps. The amount of forest cover in the study plot of 110 km² was only 10 %. For 10 forest fragments the frequency of occupation increased significantly with the decreasing size of the fragments. The presence of breeding pairs of Common Buzzards did not significantly affect the frequency of occupation of 10 fragments of <27 ha. Additionally, for fragments occupied by both species, there was no significant increase in the occupation by Honey Buzzards with inreasing patch size. Both species used to breed successfully alongside each other in small patches. The number of rain days in May had no significant impact on the density during the study period. Similarly, I confirmed at least 4–6 successful broods each year. I conclude that forest fragmentation does not carry any threat to the Honey Buzzard population. Mechanisms like competition, habitat fragmentation and climate seem to act through food supply.