Speckled Worm Eel (Myrophis Punctatus) in the Estuarine Waters of Texas: A “Dove Tale” of the Elusive American Eel (Anguilla Rostrata)

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2020-05-08
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Abstract

Atlantic Anguillids share unique life histories where they undergo metamorphosis as they move from deep water to near shore habitats, though their life history strategies differ slightly; some of the primary mechanisms driving their distribution and recruitment are the same. The juvenile American Eel (Anguilla rostrata), a catadromous species, was targeted for this study. Historically, all American Eel life stages have been subjected to commercial fishing pressure and dramatic reductions have been observed in indices of their abundance. The Gulf of Mexico is data deficient with respect to early life history of this unique species, and more specifically the Texas coast. The central and upper Texas coastal marsh and estuarine habitats were targeted for this study to detect ingressing glass eels as they settle in the coastal habitats and eventually pursue upstream migration. In an unexpected turn of events, juvenile American Eel were not captured; however, Speckled Worm Eel (Myrophis punctatus) were captured every month of the study period from July 2018 to July 2019 using modified fyke nets as the standard sampling technique. Furthermore, metamorphic, glass and elver life stages were detected with the early life stages appearing in estuarine waters in December 2018 and peaking in February and March of 2019, suggesting recruitment of Speckled Worm Eel occurs in the winter and spring months along the Texas Coast. Though consistently captured, there was high spatial variability in catch per unit effort across coastal sub basins (CPUESB) defined by total Speckled Worm Eel captured divided by cumulative hours fished within each sub basin. The highest CPUESB sampled were Matagorda Bay (4.050), Brazos River (2.879) Galveston Bay (0.203), and Sabine Lake (0.223). The occurrence of Speckled Worm Eel was modeled using Binomial Logistic Regression with various predictors. Regression results indicated significant negative relationships between occurrence with Secchi depth (m) a proxy for water clarity, and water temperature (℃), and a positive relationship with salinity (psu). As Speckled Worm Eel metamorphosed to elvers, morphometric comparisons revealed dramatic increases in average head length from 5% to 10% of their total length, decrease average body depth as a ratio of total length from 4.3% to 2.4%, and no change in the average preanal length by total length ratio. Weight length relationships were characterized by a non-linear power model relationship W=aLb and shows that metamorphic life stage (b =2.666) displayed reverse negative allometric growth (body shrinkage), while glass eel (b =2.917) and elver (b = 3.013) both displayed isometric growth. As a species, positive allometric growth is observed (b = 3.127). The results presented in this study help to better characterize the life history of a very cryptic species along the Texas coast, which may be underrepresented in catches by state fisheries independent monitoring programs. The results of this study contribute to the knowledge base of the species as a whole and supports the notion that fyke nets are an excellent passive method for detecting Anguillids at all life stages. Furthermore, the effectiveness of the fyke nets in collecting Speckled Worm Eel suggests that the observed zero CPUE of American Eels is likely due to the true absence of this species and not due to gear selectivity or active avoidance.

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Keywords
Speckled Worm Eel, American Eel, Fyke Nets, Estuarine Ecology, Length-Weight, Metamorphoses, Morphometrics
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