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A preliminary ichthyoplankton survey of the Tsitsikamma National Park

Keywords: ichthyoplankton survey , bongo nets , Tsitsikamma National Park , Engraulid larvae , sparids , blenniids , plankton , plankton volume , egg and larval abundance

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Abstract:

ENGLISH ABSTRACT: An ichthyoplankton survey using bongo nets was conducted within the Tsitsikamma National Park over an 18-month period between January 1991 and July 1992. Four sampling stations along the coast were chosen, approximately 5 km apart. At each station four samples were taken along a transect perpendicular to the coast, between 0,35 km and 3,8 km offshore. Horizontal tows were taken at three and 15 m below the surface over reef and sand substrata respectively. Larvae belonging to 24 of the 35 families and 55 of the 97 species known to occur in the area were captured. Engraulid larvae completely dominated the catches while amongst the reef-associated taxa sparids and blenniids were prominent. Seasonally occurring cold upwelling event impacted negatively on egg and larval abundance. Mean values for egg and larval abundances were 1207 and 282 per 100m3 respectively. A relationship between larval number and plankton volume was revealed. Most larvae captured were between 2,0 and 20,3 mm (SL), and in the preflexion condition. The absence of larger size classes in samples was attributed to net avoidance. AFRIKAANSE OPSOMMING: 'n lgtioplankton-opname is oor 'n tydperk van 18 maande, tussen Januarie 1991 en Julie 1992 binne die Tsitsikamma Nasionale Park (TNP) gedoen met die gebruik van bongo-nette. Vier stasies is langs die kus gekies, ongeveer 5km uitmekaar. By elke stasie is vier monsters op ‘n lyn loodreg met die kus tussen 0,35 km en 3,8 km vanaf die strand geneem. Die nette is horisontaal getreil drie en 15 m onder die oppervlak en monsters is onderskeidelik oor sand een rif geneem. Larwes van 24 uit die 35 families en van 55 uit die 97 spesies wat in die TNP voorkom is gevang. Die familie Engraulidae het die vangste oorheers terwyl die Sparidae en Blenniidae prominent was onder die rifverwante visse. Seisoenale koue opwellings het 'n negatiewe uitwerking gehad op die hoeveelheid eiers en larwes. Gemiddelde waardes vir onderskeidelik eier- en larfhoeveelhede was 1207 en 282 per 100 m3. 'n Verwantskap tussen die larfhoeveelhede en planktonvolume is opgemerk. Die meeste van die larwes in die monsters was tussen 2,0 en 20,3 mm lank (SL) en in die voorverbuigingsvorm. Die afwesigheid van die groter klasgroottes is aan netontduiking toegeskryf.

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