Abstract:
The purpose of this investigation was to understand how symbiotic sharksucker-host
interactions may have shaped life history characteristics of the symbiont. Here, I
examined growth, trophic ecology, and reproduction of Sharksucker, Echeneis naucrates,
in the northeastern Gulf of Mexico. Age was determined from otoliths, and growth (in
standard length, SL) was modeled as a von Bertalanffy function. Males and females grew
at similar rates (K = 0.54 and 0.51 year-1, respectively), but asymptotic length was
significantly higher in females (L∞ = 514 mm) than males (L∞ = 445 mm). Diet varied
by size group. Ectoparasitic copepods and other small crustaceans were the most
frequently occurring item (78%) in the stomachs of small (<249 mm SL) sharksuckers,
and fish was the second most frequent item (46%). Large sharksuckers consumed
crustaceans less frequently (31%) and fish more frequently (60%). Crustaceans
comprised a higher mean proportion of volume (MV) of small sharksucker diet (54% vs. 13%), and MV of fish was lower (15% vs. 32%). Sharksucker stable isotope N and C
values exhibited significant trends with body size by location. Small (<249 mm SL)
sharksuckers were enriched in δ13C and depleted in δ15N. Further, those from the Big
Bend area were depleted in δ13C and δ15N relative to samples from the Florida Keys.
Gonad histology indicated that sharksucker are indeterminate batch spawners with a peak
reproductive period in the late summer in the northeast Gulf of Mexico. Gonadosomatic
indices peaked for both male and female sharksuckers in August. Mean relative batch
fecundities estimated from hydrated oocytes was 42.0 hydrated oocytes per gram ovaryfree
body weight (OFBW). Due to unique life history adaptations, this symbiotic species
appears particularly vulnerable to host availability during critical life stages. Thus, the
conservation status of host species (i.e., sharks), which are in decline in many regions, is
intimately tied to the population status of the sharksucker.
