MEPS 187:213-225 (1999)  -  doi:10.3354/meps187213

Distribution and feeding of blue whiting Micromesistius poutassou larvae in relation to different water masses in the Porcupine Bank area, west of Ireland

Nicola Hillgruber1,*, Matthias Kloppmann2

1Biologische Anstalt Helgoland in der Stiftung Alfred-Wegener-Institut für Polar- und Meeresforschung, Notkestrasse 31, 22607 Hamburg, Germany
2Institut für Hydrobiologie und Fischereiwissenschaft, Universität Hamburg, Olbersweg 24, 22767 Hamburg, Germany

ABSTRACT: In March/April 1994 a hydrographic and ichthyoplankton survey was conducted in the area of Porcupine Bank, west of Ireland, to study the distribution and feeding of blue whiting larvae. The Porcupine Bank area was characterized by 2 distinguishable water masses separated by a thermal front: (1) the warm and saline waters of the secondary shelf edge current (sSEC) and (2) the cooler and less saline waters above Porcupine Bank associated with an anticyclonic circulation. Highest concentrations of recently hatched larvae <4.0 mm standard length (SL) occurred in waters of the sSEC, while larvae >4.0 mm SL were more abundant in the cool waters above Porcupine Bank and larvae >5.0 mm SL were exclusively found above the bank. Copepod nauplii density was extremely low, with an overall mean density of 5.2 l-1. Nauplii were most abundant in the water of the sSEC. However, proportionally more large calanoid nauplii were observed above Porcupine Bank. The diet of blue whiting larvae also varied among water masses, with larvae having higher feeding incidences and numerical feeding intensities in the sSEC but significantly higher feeding intensities by weight and, thus, a higher energetic gain in the waters above the bank. These contrasts resulted from differences in the composition of the larval diet. Larvae in the sSEC preyed heavily on tintinnids and small cyclopoid nauplii, while larvae above Porcupine Bank also ingested large calanoid nauplii. In addition, blue whiting larvae had different selectivity patterns depending on the foraging environment, with larvae retained above Porcupine Bank selecting strongly for calanoid nauplii, which were never selected for by larvae in the sSEC. Instead those larvae demonstrated a preference for smaller cyclopoid nauplii. In summary, we conclude that in 1994 blue whiting larvae benefited from being retained above Porcupine Bank not only by maintaining a close horizontal distribution but also by utilizing the more favorable feeding environment above the bank.

KEY WORDS: Blue whiting larvae · Distribution · Diet · Feeding success · Prey selection · Retention

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