Life History Bio-Sampling Progressing in American Samoa, CNMI and Guam

The PIFSC Commercial Fisheries Bio-Sampling (CFBS) project was created to provide key biological information to support fish stock assessments across the U.S. Pacific Islands Region. The project involves contracted bio-sampling teams operating in American Samoa, Commonwealth of the Northern Mariana Islands (CNMI), and Guam. These teams collect biological data from fish species important to the island regions whose life history remains little known. Length and weight measurements for all fish species are collected regularly from a fishermen's cooperative on Guam and local vendors and fish markets surveyed in American Samoa and CNMI. In each of these jurisdictions, 3-10 selected species are targeted for life history sampling. Biosamplers collect otoliths and gonads from individual fish, along with measurements of fish size, for studies to determine length-at-age relationships and size at 50% reproductive maturity for each species. Sampling for life history studies needs to 1) be representative for a species over the range of available sizes, 2) across most if not all months, and 3) include both the immature and spawning portions of the population.

Initial processing of otoliths for age and growth studies has been completed by two contracted otolith preparation services. A subsample of otoliths from eight species, across a range of sizes, was cross-sectioned to evaluate the readability of the presumed annual growth zones. This work will help us determine which species are amendable to ageing techniques based on growth zone enumeration.

For the size at maturity studies, we have developed plots of the ratio of gonad weight to body weight (known as gonadal somatic indices or GSI) by month and sex for the selected species. The GSI plots provide us an estimate of the spawning season, indicate whether immature individuals and spawners are represented in the sampling, and reveal any temporal or size gaps in the sampling.

Processing of preserved gonad samples into stained histology slides is conducted through a contract with the University of Hawaii Medical School. So far gonad histology slides have been prepared for 295 gonads from American Samoa, 797 gonads from CNMI, and 443 gonads from Guam. These slides currently await analysis. By analyzing the histology slides, we will be able to determine gender, identify the reproductive phase of the gonad, and distinguish between the immature and resting mature phases.

The following table reports the numbers of otolith samples, gonad samples, and length measurements collected to date for the 18 species targeted for life history studies.

Species Targeted for Life History Sampling Number Collected from CNMI Number Collected from Guam Number Collected from American Samoa
  Otoliths Gonads Lengths Otoliths Gonads Lengths Otoliths Gonads Lengths
Cheilinus undulates 1 1 177 50 53 61 0 0 17
Etelis coruscans 0 0 178 270 268 238 0 0 74
Hipposcarus longiceps 0 0 1141 164 163 1666 0 0 22
Lethrinus atkinsoni 495 495 2034 7 7 923 0 0 1
Lethrinus xanthochilus 0 0 194 0 0 212 215 216 929
Lutjanus gibbus 0 0 150 4 2 1060 200 200 892
Lutjanus rufolineatus 0 0 0 0 0 0 156 156 330
Monotaxis grandoculis 0 0 380 143 123 1497 0 0 174
Myripristis amaena 0 0 297 0 0 7 189 188 1241
Myripristis berndti 0 0 765 5 5 2103 342 334 1604
Myripristis murdjan 0 0 1241 0 0 144 216 211 859
Naso unicornis 523 523 3492 16 11 9959 270 272 2309
Parupeneus barberinus 728 728 2965 0 0 729 0 0 29
Sargocentron spiniferum 0 0 874 2 0 460 115 114 224
Sargocentron tiere 0 0 657 4 2 313 471 425 3854
Scarus rubroviolaceus 0 0 1641 0 0 1632 188 194 2008
Variola louti 0 0 1 129 128 612 0 0 165