SEMINAR: MBF STUDENT SEMINAR --TOMORROW @ 12N-- Mark Fitchett, Ilan Ruhr, and Matt Nuttal

[Pam Harris <pharris@rsmas.miami.edu>]

  PLEASE NOTE THERE IS NO FACULTY SEMINAR SCHEDULED.

 

MBF Student Seminar Series

Mark Fitchett

Advisor: Dr. Nelson Ehrhardt

“Improving the development of age-length keys in data-poor fisheries:

the eastern Pacific sailfish as a case study.”

Age-length keys (ALKs) are distributions of age at length used to estimate catch-at-age from length-frequencies in total landings. Catch at age information is needed in cohort analyses for assessing status of species abundance and exploitation. Istiophorid billfishes (sailfish, black marlins, blue marlin, striped marlin) in the eastern tropical Pacific are heavily exploited as bycatch in longline and purse seine fisheries targeting tunas. Billfish catches are incompletely reported and biological hard parts for ageing throughout the distribution of these species are not readily available. In data-poor fisheries where reliable ALKs are absent, length-frequency data are “sliced” into ages by a growth function. This approach does not take into account true variability of size-at-age and tends to overestimate mortality rates and underestimate abundance. In this seminar I will present a method in contrast to slicing procedures that follows groups of fish throughout time within size-at-age bins using variance and covariance of growth parameters. Knowledge on the variance of size at age under given exploitation patterns contributes to a better distribution of age frequencies within length bins. Therefore, a numerical solution to an ALK approximation may significantly contribute to better estimates of fishing mortality and abundance in data-poor fisheries.

 

Ilan Ruhr

Advisor: Dr. Martin Grosell

“Guanylin-regulated transport in the intestinal epithelia of the Gulf Toadfish (Opsanus beta).”

The homologous peptides, guanylin (GN) and uroguanylin (UGN), are upstream regulators of the cystic fibrosis transmembrane conductance regulator (CFTR) channel. In mammals, CFTR activation allows Cl- secretion into the lumen of the intestine, which allows water to follow osmotically. These peptides also increase bicarbonate secretion into the lumen, which helps maintain intestinal pH in response to acidic chyme from the stomach. However, the physiological effects of GN and UGN on water and electrolyte transport in marine teleost fish intestines have yet to be studied. GN, UGN, and Renoguanylin (RGN; a homologue of the former two) were used to determine the effects on the short-circuit current (ISC), and the transport of bicarbonate and water in the gulf toadfish (Opsanus beta). Ussing chambers, a pH-stat titration system, and gut sac experiments where used to determine the physiological effects of the peptides. GN, UGN, and RGN reversed the ISC of the posterior intestine (absorptive-to-secretory), but not of the anterior intestine. In contrast to mammals, RGN either decreased or maintained baseline bicarbonate secretion, but did increase water and Cl- secretion into the lumen of the posterior intestine. These data suggest that marine teleosts may possess a tissue-specific secretory response that could be useful for flushing the intestines of toxins, undigested food particles, or calcium carbonate precipitates that are naturally formed in the intestines as part of osmoregulatory processes.

 

Matthew Nuttal

Advisor: Dr. Elizabeth Babcock

“Historical recount of the Great South Bay ecosystem, Long Island, New York and a quantitative assessment of the ecosystem structure of Great South Bay using Ecopath.”

The Great South Bay (GSB) ecosystem has provided marine resources to Long Island residents for well over 300 years.  However, various external stressors have threatened this system and there are declines in multiple stocks and ecosystem indices.  A historical review was conducted.  Of the twelve stocks with identifiable temporal abundance trends, eight are currently declining in both abundance and recent harvests by GSB fisheries.  In addition to monetary losses to local fishermen, the lack of a commercially dominant shellfish stock may leave GSB without a dominant filter feeder, facilitating the brown tide blooms that have affected stocks of plankton, shellfish, finfish, and eelgrass since 1985.  Ecopath (mass-balanced food web) models were developed to elucidate ecosystem structure and function and indicated GSB has seen concurrent drops in ecosystem size and maturity.  Twenty two of the twenty four ecosystem maturity indices measured an overall drop.  Trends consistent with habitat degradation, alterations to physical conditions, phosphorus loading, and overfishing were observed. Whether these system stressors caused the observed changes in ecosystem structure is unknown, but this modeling exercise can enhance restoration by providing an understanding of system changes and historical baselines.

 

FRIDAY, APRIL 12, 2013

12N

RSMAS campus, S/A 103

Pamela Harris

Marine Biology and Fisheries

Rosenstiel School of Marine & Atmospheric Science

University of Miami

4600 Rickenbacker Causeway/SLAB-118

Miami, FL 33149

(305) 421-4176

fax - (305) 421-4600

pharris@rsmas.miami.edu  

 

http://www.rsmas.miami.edu/academics/divisions/marine-biology-fisheries/