Spring Distribution Of Zooplankton and Larvae Within Elephant Butte Reservoir, New Mexico

Elephant Butte Reservoir is New Mexico’s most highly utilized recreational sport fishery.  Historically, the stocking method utilized at Elephant Butte Reservoir marginalized the importance of prey base dynamics.  As biologists we understand that stocking success depends upon a multitude of factors including the what, when, and where prey is available.  Zooplankton and larval populations were sampled and analyzed.  These analyses brought to light these crucial prey dynamics and allowed for the development of stocking strategies that will assist in maximizing our limited resources.  Gizzard shad (Dorosoma cepedianum) was the primary species captured with the larval tows, however other species were collected as well.  Neither zooplankton nor larval gizzard shad were evenly distributed throughout the reservoir.  Throughout the sampling period (April – July) larval gizzard shad are much more abundant in the north end of the reservoir (df =4, P=0.000) than in the south end.  In early spring, the north end warms up much more rapidly and completely mixes while the south end stays cooler and stratified.  Zooplankton populations appear to peak and crash with what appears to be little influence of larval competition.  Based upon the results a stocking matrix was developed to assist when determining stocking dates, locations, and species to be stocked.