Graduation Year

2025

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Degree Granting Department

Marine Science

Major Professor

Steven Murawski, Ph.D.

Co-Major Professor

Heather Judkins, Ph.D.

Committee Member

Isabel Romero, Ph.D.

Keywords

BMF, OCP, PAH, PCB, squid, tuna

Abstract

Cephalopods are an important component of pelagic food webs. They play ecological roles not only as predators but also as prey. However, their role as prey in the trophic transfer of organic contaminants to apex predators such as tunas in the Gulf of Mexico (GoM) is not well known. To investigate the importance of cephalopods in tuna diets, stomach samples were collected in February 2020 from tunas caught by rod and reel aboard the F/V Gulf Eagle near two large offshore floating oil/gas platforms in the northwestern GoM. Cephalopod samples were obtained from gut content analysis of 41 tunas caught during the cruise. My study examined the concentration and composition of 159 targeted organic contaminants by predator species and prey species. I compared liver and muscle tissues of 15 Blackfin Tuna (Thunnus atlanticus) and 10 Yellowfin Tuna (Thunnus albacares) and the mantle tissue of 20 cephalopods from their stomach contents. In particular, the prey analyses focused on the Common Clubhook squid, Onychoteuthis banksii, because of its prevalence in tuna stomachs. I quantified oil-derived polycyclic aromatic hydrocarbons (PAHs) and their oxidation products (OPAHs), polychlorinated biphenyls (PCBs), organochlorinated pesticides (OCPs), and emerging contaminants of concern (ECCs). Analysis was completed using accelerated solvent extraction (ASE) with gas chromatography and tandem mass spectrometry in multiple monitoring reaction mode (GC/MS/MS/MRM).This study found that the mean total concentrations in all tissue types (mantle, liver, and muscle) followed the same trend (∑ECCs > ∑PAHs > ∑OCPs > ∑PCBs), except in Blackfin Tuna muscle tissue (∑ECCs > ∑PAHs > ∑PCBs > ∑OCPs). PAH sourcing predominantly identified petrogenic sources for all species. Both tuna demonstrated that OPAHs were products of PAH metabolism. Opposite trends in lipid storage were observed between tuna liver and muscle tissue, which may relate to behavioral and metabolic differences between the species. Compound group correlations with lipids and standard length (SL) indicated bioaccumulation of ∑PCBs and ∑OCPs in Blackfin Tuna and ∑ECCs in Yellowfin Tuna. Squid discovered in Blackfin Tuna were smaller compared to those in Yellowfin Tuna. The squid from Blackfin Tuna stomachs exhibited significantly higher ∑PAHs and ∑OCPs than those from Yellowfin Tuna stomachs. There was a negative correlation between mantle length (ML) and ∑PAHs as well as ∑OCPs, indicating a growth-dilution effect for the Common Clubhook Squid. The mean trophic position for Blackfin Tuna (3.95) and Yellowfin Tuna (4.03) aligns with findings from other studies. Biomagnification factors of the tuna/squid food web based on trophic level indicated that the highest BMF values were consistent for both tuna: PCBs (82, 187, 183), Metolachlor (OCP), and benzo(b)fluoranthene (PAH), which supports evidence of biomagnification of these analytes in other results. Overall, this study indicates that tuna are capable of metabolizing or excreting the majority of organic contaminants examined.

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