Breeding patterns of shark populations in Moorea Island
The collapse of shark populations has resulted from the difficulties of shark recruitment to keep up with the over-exploitation they are experiencing worldwide (high fishing pressure and habitat degradation). Sharks are particularly vulnerable to overexploitation due to their reproductive characteristics (e.g., low fecundity and late age at maturity) which are more similar to that of mammals than teleost fishes. There is little information available on mating systems, reproductive mechanisms, genetic basis of parentage in sharks and population turnover.
RECRUITMENT, TURNOVER AND SELF-RECRUITMENT OF SHARK POPULATIONS IN MOOREA ISLAND
Knowledge of genetic structure of population is important for implementation of conservation plans. Unlike coral fish, reef sharks give birth to few pups autonomous that will grow alone in shark nurseries. Only adult individuals have the ability of dispersal by migrating to reproduce with other populations. Where coastal sharks are giving birth, as well as whether or not they show philopatry to specific nursery sites has important implications for the spatial scale of their management and conservation.
Direct estimates of breeding patterns and connectivity in reef-associated sharks are essential to understand their population dynamic and adapt or optimize the conservation strategies for these endangered marine predators. While there have been some attempts to investigate breeding patterns of reef sharks from litter reconstruction by molecular analyses, direct fine scale dispersal conducted by females during parturition as well as connectivity between islands has never been assessed. Here we used microsatellite DNA markers and a likelihood-based parentage analysis to assess the breeding patterns of female blacktip reef sharks in a Polynesian island.
The use of genetic tools such as microsatellite markers and parentage analysis allows me to analyse the recruitment of shark populations as well as the population structure by studying parentage links between individuals of the population. These analyses allows me infering self-recruitment rate and percentage of inbreeding in these shark populations and in the end investigating their degree of genetic vulnerability. Thus the spatial scale of gene flow, the connectivity and the self-recruitment rate can be assess for both species sicklefin lemon sharks and blackfin reef sharks in Moorea. This kind of analysis requires sampling most of the individual of the population and their recruits.
The aim of this study is to apply parentage analysis based on hyper-variable microsatellite DNA markers to investigate processes of recruitment and connectivity led by female sharks as well as mating patterns. The approach is based on the identification of offspring produced by genotyped adults from the island. Providing the location of adults and juveniles is known or can be assumed due to the restricted home range of adults and the sedentary behaviour of juveniles within their nursery, the dispersal process conducted by females to give birth in specific locations can be investigate. These data represent the first direct estimates of the breeding patterns of females and local connectivity of sharks.
Methods:
•Skin sampling on free living sharks (with a tipped modified spear gun or caught by fishing)
•Development of microsatellite markers for C. melanopterus and N. acutidens
•Parentage analysis to determine population turnover
Biopsy techniques used for skin samples:
For genetic analysis, we need to collect pea-sized tissue samples containing DNA from the shark. To collect these samples, we use different techniques depending on the shark species we want to sample and its size.
Adult lemon sharks (from 2 to 3 metres total length) were sampled using a biopsy tip mounted on the end of a spear gun, as shown in the film bellow. No sharks are harmed with this technique and are not sampled more than once.
Juvenile sharks (sicklefin lemon sharks as well as blackfin reef) sharks are fished at dawn in the shallow waters of their nurseries. For that, I use gillnets and handlines with barbless hooks. When caught, sharks are brought back to the shore to measure their length, determine the sex and cut a fin clip. They are then released in the water. Some adult blacktip reef sharks are also caugth inside the lagoon with this technique.
Adult blackfin reef sharks are also fished from a boat in different places of the Island with a fishing rod and are immobilised along the boat to measure shark length, determine the sex and cut a fin clip before releasing them.
Main results:
Visual monitoring of pregnancy
Coming soon…
