Boaz Kaunda-Arara

Out-migration of tagged fishes from marine reef National Parks to fisheries in coastal Kenya

We evaluated movements of 25 species of coral reef fishes from Malindi and Watamu Marine National Parks (created 1968) in coastal Kenya from February 2001 to March 2002. Only three species, the commercially important whitespotted rabbitfish, Siganus sutor, the sky emperor (SEM), Lethrinus mahsena and the trumpet emperor, L. miniatus, exhibited consistent movements from the parks. At Malindi Park, more fishes were recaptured by fishermen off a fringing reef than off a patch reef. The rabbitfish had a higher monthly spillover rate from the fringing reef than from the patch reef. In contrast, the SEM had low monthly spillover rates from both reefs. The rabbitfish moved greater distances off the fringing reef than off the patch reef. At Watamu Park, the SEM, L. miniatus and the gold-spotted sweetlips, Gaterin flavomaculatus, had equal monthly spillover rates. In contrast, the rabbitfish had a lower monthly rate. The emperors showed no difference in net distance moved from the park boundary, however, L. miniatus traveled significantly longer distances than did the SEM. Distances between release and capture sites were either random (SEM), increasing (L. miniatus), or decreasing (rabbitfish) with respect to time at liberty.

Long-distance movements of coral reef fishes

Most coral reef fishes are thought to be highly sedentary with movements limited to a few kilometers for even the most mobile species (Holland et al. 1996; Zeller 1997). Long distance (>200 km) movements to spawning aggregations have been reported for Epinephelus striatus (Nassau grouper) often with return to home reefs. Other reports on large spatial-scale movements in tropical fishes have been limited to pelagic and non-typical reef species like the blue runner, Caranx fuses (155 km) (Beaumariage 1964) and the blue trevally, Caranx melampygus (72 km) (Holland et al. 1996). Movements are demanding in energy requirements (Bernstein et al. 1991) and are not without functional role. Among coral reef fishes, local movements have been associated with feeding, spawning, and ontogenetic shifts in habitat requirements (Sale 2002). Additionally, movements may ensure connectivity between stocks. However, a major unanswered question in marine ecology is the degree of connectedness between populations (Robert et al. 2000). In coral reef environments, the open nature of reproduction in most fishes has made pelagic larval dispersal the dominant linkage between reef fish populations (Cowen et al. 2000). However, active adult dispersal between source and sink populations (Crowder et al. 2000) may complement larval dispersal in maintaining connectivity between populations and is thought to be a more stable mechanism evolutionarily (Holt 1996). In this paper we document long-distance movements in three species of coral reef fishes.

Daily Growth of Young-of-the-Year of the Baringo Tilapia, Oreochromis Niloticus baringoensis (Trewavas, 1983)

Otolith microstructure analysis was used to validate microincrement deposition rate and to determine daily growth rates of young-of-the-year (YOY) Baringo tilapia, Oreochromis niloticus baringoensis. Micro-increment formation was validated as daily by correlating the number of circuli on otoliths with the known age of cultured fish. For wild young-of-the-year fish collected from Lake Baringo, Kenya, in August and October 2007 length was positively correlated with the age of fish (total length (mm) = 0.1187 age (/day) + 1.1344 (r2 = 0.97); standard length (mm) = 0.0964 age (/day) + 0.7082 (r2 = 0.97)) and growth rate was subsequently estimated at 0.12 cm/day.

Alongshore distribution and abundance of fish larvae off the coast of Kenya

Knowledge is limited on the fish larval assemblage in shallow lagoonal reefs along the Kenyan coast. Fish larvae from five lagoons, spanning 120 km on the Kenyan coast, were sampled in March 2007 and April 2008 to compare interannual spatial variations in species composition, abundance and diversity along the coast. In all, 2 644 fish larvae were sampled, comprising 26 families and 37 species in 2007 and 43 families and 73 species in 2008. The larval assemblage was dominated by Gobiidae, Blenniidae, Pomacentridae and Gerreidae during both years. Larvae hatched from non-pelagic mode of spawning constituting 92% of total numbers. Mean larval abundance (no. 100 m−3 ± SE) along the coast ranged from 5.0 ± 1.0 to 414 ± 226, with highest densities occurring on the northern sites of Watamu (414 ± 226) and Malindi (31 ± 10). Interannual variation in larval abundance between 2007 (2.17 ± 0.3) and 2008 (2.16 ± 0.1) was not significant (p > 0.05). Shannon-Wiener species diversities between sites ranged from 1.2 ± 0.4 to 2.3 ± 0.3, with highest diversities occurring in Mombasa (2.2 ± 0.5) and Nyali (2.3 ± 0.3). In 2007, the occurrence of preflexion larvae increased northwards from Mombasa (18.2%) to Watamu (86.4%), whereas in 2008, the reverse was the case with the incidence of preflexion larvae reducing northwards from Mombasa Marine Park (76%) to Watamu Marine Park (2%). These trends indicate interannual variation in larval source sites for fish species. Correspondence analysis revealed distinct larval assemblages at sites along the coast, which varied between years.