Reproductive Dynamics of Sheepshead in South Texas

Figure 1. Picture of sheepshead

Sheepshead (Archosargus probatocephalus) is an abundant, coastal fish species in the northern Gulf of Mexico and an important component of inshore recreational fisheries in Texas. Despite their high proportion of landings, little is known about the life history traits, spawning behavior, or population structure of Sheepshead in the region.

Sheepshead samples are collected daily to weekly from local fillet stations from December through June to assess temporal spawning patterns in relation to local environmental conditions. Gonads are visually assessed based on their coloration, size, vascularization, and visibility of their eggs. Actively spawning females possess large, yellow gonads with translucent eggs, while actively spawning males freely release milt. Visual and microscopic assessments of gonadal development in females indicate that spawning begins in late February and continues through early April.

Figure 2. Female gonads. From left to right: developing female gonads, spawning capable female gonads, actively spawning female gonads, and regressing female gonads.

Figure 3. Monthly percentages of Sheepshead at each gonadal stage observed within the spawning season from 2016 to 2017. Data for 2017 was collected up to April 19.

 

Spawning activity is influenced by local water temperatures, as spawning begins each year when temperature reach about 20 degrees Celsius. Spawning occurs on a daily basis from early March through mid April, with some limited evidence that spawning activity peaks during first quarter and full moons.

 

Figure 4. Average daily water temperature during the 2016 and 2017 spawning season. For both years, spawning began when the water temperature was 19.7°C, as indicated by the colored arrow.

 

Data from NOAA’s marine recreational information program (MRIP) indicates that recreational Sheepshead catch in Texas peaks during March and April. Recreational anglers target sheepshead pre-spawning and spawning aggregations that form at the mouths of shipping channels and at nearshore oil platforms during this period. On average, more than 60% of the total annual landings of Sheepshead occur at spawning sites during their peak spawning season in March and April, and large numbers of adults are also harvested from their pre-spawning aggregations that form in late December through February.

Figure 5. Top ten most abundant annual fish landings in Texas from 2010-2015.

 

Figure 6. Study site in Port Aransas, Texas. Sheepshead form spawning aggregations in the spring at the mouth of the ship channel (indicated by the red star,) and at nearshore oil platforms.

We have also been monitoring local fillet stations to assess the proportion of the total recreational catch that is comprised of Sheepshead. Our preliminary results indicate that the highest proportions of Sheepshead occur during February through March in association with both their pre-spawning and spawning aggregation periods. Landings steadily decline from April through June as aggregations disperse and anglers shift their effort towards Spotted Seatrout, Red Drum, and other game fishes. Sheepshead aggregations can be very large (thousands of fish) and are easily accessed by recreational anglers, which explains why Sheepshead represent the dominant species in the nearshore recreational fishery in Port Aransas from January through April.