Relationship between Gulf Menhaden Recruitment and Mississippi River Flow: Model Development and Potential Application for Management

Abstract

The Gulf menhaden Brevoortia patronus is one of the most abundant pelagic fishes in the northern coastal Gulf of Mexico (hereafter, "Gulf") and is the principal forage for various commercial and sport fishes, sea birds, and marine mammals. Part of the life history of Gulf menhaden is spent on the continental shelf and part is spent within estuaries. Adults spawn near the mouth of the Mississippi River, and larvae aggregate within the river plume front. Larval Gulf menhaden transit the continental shelf and enter estuaries of the northern Gulf as juveniles. Govoni (1997) demonstrated an association between the discharge of the Mississippi and Atchafalaya rivers and Gulf menhaden recruitment. In particular, he found an inverse association between Mississippi River discharge and estimated recruitment of half-year-old fish based on recruitment data from Vaughan et al. (1996). Vaughan et al. (2000) updated this relationship with a regression analysis. Here, we revisit the relationship with additional years of data through 2004. The inverse relationship continues to hold. In addition, we reframed this relationship to produce a 1-year-ahead prediction model for forecasting recruitment to age 1 from Mississippi River discharge; this model can be used in proactive fishery management. Finally, we revisited the stock assessment model of Vaughan et al. (2007) and demonstrated an improvement in model performance when information on annual river discharge was incorporated.The Gulf menhaden Brevoortia patronus is an exploited marine resource as well as an integral and key ecological component of the coastal northern Gulf of Mexico (hereafter, "Gulf")

Anomalously High Recruitment of the 2010 Gulf Menhaden (Brevoortia patronus) Year Class: Evidence of Indirect Effects from the Deepwater Horizon Blowout in the Gulf of Mexico

“…Govoni (1997) found that annual Mississippi River discharge was negatively associated with numbers of half-year recruits, and suggested that higher discharges result in an expansive plume, which may propel larvae further offshore and delay the shoreward transport of larvae, hence increasing their vulnerability to predation. Historically, mean monthly discharges of the Mississippi and Atchafalaya Rivers from November through March accounted for nearly 30% of Gulf menhaden recruitment variability in regression analyses (Guillory et al 1983; Vaughan et al 2011). Hence, the oceanographic conditions during winter and spring 2010 should have lowered recruitment of the 2010 Gulf menhaden year class, partially or even entirely offsetting the effects of favorable phytoplankton abundance.

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Macroscale drivers of Atlantic and Gulf Menhaden growth

“…In the Gulf of Mexico, both a juvenile and adult index of abundance were excluded as predictors due to the limited number of years available. We derived a time series of river discharge ( River Discharge ) for the Gulf of Mexico using annual discharge rates based on the Mississippi and Atchafalaya River flows during the winter months as described in Govoni () and Vaughan et al (). Daily discharge was obtained from the Tarbert Landing gauge located at river mile 306.3 and the Simmesport gauge at river mile 4.9.…”

“…Further complicating any understanding of the primary drivers of fish growth is that environmental conditions may operate and interact at different temporal and spatial scales. As an example of the difficulty disentangling factors, in the northern Gulf of Mexico the timing and magnitude of Mississippi River flow affects Gulf Menhaden Brevoortia patronus recruitment, resulting in potential annual variation that could be caused by a changing climate, short‐term variations in river flow, timing of spring thaws, broadscale environmental factors, and landings (Govoni, ; Sanchez‐Rubio & Perry, ; Vaughan, Govoni, & Shertzer, ). All of these factors could also affect growth, and the relative contribution of any one factor may be difficult to quantify.…”

Ecosystem‐based forecasts of recruitment in two menhaden species

“…The results for Gulf menhaden agree with previous analysis showing that environmental drivers are important for understanding recruitment variability. Previous studies have focused on the effect of Mississippi and Atchafalaya river outflow (Govoni, ; Vaughan et al., ) on recruitment. These analyses, however, were based on stock assessments including adult landings data with assumptions such as the natural mortality of menhaden being constant across all years (i.e., independent of ecosystem processes).…”

“…For menhaden, there are particular problems stemming from the fact that observational programmes responsible for measuring menhaden juveniles are largely designed around other species (e.g., striped bass). Strong dependence on stochastic environmental drivers is also a common explanation, with studies across both species identifying a wide array of processes that—at least at one time or another—affect recruitment, including longshore wind patterns (Quinlan, Blanton, Miller, & Werner, ), winter storms (Checkley, Raman, Maillet, & Mason, ) and river flow (Govoni, ; Sanchez‐Rubio & Perry, ; Vaughan, Govoni, & Shertzer, ). However, attempts to incorporate environmental information into recruitment forecasts via the traditional “environmental Ricker” (Nelson, Ingham, & Schaaf, ) have not met with much success (Myers, ).…”