Going Vertical for Red Snapper

Honestly, it’s hard to drop a hook down on any of the natural or artificial reef habitats in the Gulf of Mexico (GOM) without catching a red snapper. Well, what happens when you drop 30 hooks down? How many red snapper do you catch? How big are they? Are there more on certain habitats? We are headed into the Gulf of Mexico off Texas to find answers to these questions on one of our vertical longline red snapper sampling trips (or VLLs).

Red snapper support an important, although highly regulated commercial and recreational fishery, and we need good data to continue to properly manage it. In both the federal Exclusive Economic Zone (EEZ, from 9 nautical miles to 200 nautical miles off the gulf beach) and Texas Territorial Seas (TTS, from the gulf beach out to 9 nautical miles), the recreational fishery is managed through bag and size limits as well as seasonal closures. In 2018, private recreational fishermen were able to enjoy extended red snapper fishing opportunities through an Exempted Fishing Permit (EFP). This EFP was managed through an agreement between Texas Parks and Wildlife Department (TPWD) and NOAA Fisheries, and allowed you to fish in the EEZ 82 days, and 365 days in the TTS and stay within our 2018 Texas quota of 241,245 lbs (or around 6% of the GOM private rec quota). In 2019 we will have another year of the EFP, putting us one step closer to regional management. Our long-term creel program surveys (along with iSnapper - iSnapper.org) provide important data for red snapper management. However, TPWD also collects data from fishery independent surveys (using our own catches with standardized gear) to compliment creel surveys.

Over the last four years, we have conducted The Southeast Area Monitoring and Assessment Program (SEAMAP) VLL survey. This is a state/federal program of the Gulf States Marine Fisheries Commission that involves using commercial-style vertical long line equipment, in a standardized way, to census red snapper populations at natural and artificial reefs along the Texas coast. Three lines with 10 hooks (30 hooks total) each spaced at 2-foot intervals are dropped to the bottom near a chosen habitat. Three different sized hooks are used (8/0, 11/0, or 15/0 circle hooks baited with appropriately sized mackerel), so we can catch a wide size range of red snapper. The vertical lines are dropped for 5 minutes, retrieved, and all fish caught are measured and weighed. Among the data yielded by this VLL method are catch rates and mean size of red snapper.

So far, we’ve sampled 186 sites (124 in federal and 62 in state waters) and deployed 5,030 hooks, which resulted in catching 879 red snapper in federal and 152 in state water on various habitats. These longlines definitely catch red snapper, which were 93% of the total catch. Of course there are other fish in the sea and we have caught twenty other species on this gear off Texas, but given the gear and bait we use, they mostly target red snapper.

We randomly select sites weighted by the percentage of habitat types (natural and artificial reefs, platforms) in three different depth zones (10-20, 20-40, 40+ meters). Not all habitats are created equal, so we need data from a variety of habitat types. Artificial reefs can vary from large cut-off/toppled platforms, to ships and wrecks, to smaller, numerous concrete pyramids (https://tpwd.texas.gov/gis/ris/artificialreefs/). We also sample large structures, such as standing platforms, as well as the much larger natural banks that have unique relief and complexity, which also hold large numbers of fish. Despite the differences and similarities between the reef types, after sampling for four years, catch patterns are starting to emerge.

One way to standardize and compare catches among the different areas and reef types is by looking at the catch per unit of effort (CPUE). Going back to answer our original question: we caught “X” number of fish with “X” number of hooks (effort). Occasionally, we drop down our baited hooks and catch nothing. It is still fishing, and you can’t catch them every time (or everywhere). More often, we will drop our hooks, get some bites, and catch some red snapper on each line, and sometimes every hook is attached to a fish.

So, how do our habitats compare in terms of CPUE? We definitely need more data to address the variability of catches across different habitats. Thus far, it appears that artificial reefs have statistically higher average catch rates (40 fish/100 hks) than natural reefs (24 fish/100 hks) in the EEZ, while the catches in TTS are generally lower (<10 fish/100 hks) and don’t significantly vary by habitat (Figure 3a). There can be a number of reasons why catch rates are greater at artificial reefs, but the main difference is reef size.

It would seem that a larger natural bank that is over 1 km wide would have more structure and more fish. That is most likely true, but those fish tend to be more spread out over that area. The smaller artificial reef may have fewer fish overall, but they are concentrated within a small area. So, when we drop the VLLs over an area of highly concentrated fish, we tend to catch more fish. And for each of the large natural banks, we sample multiple locations, so we can estimate the overall density of fish over those banks.

Interestingly, when we compare the mean total length of red snapper at those same habitats, we tend to see the opposite effect (Figure 3b). Of the sites we sampled, natural reef tended to have larger fish than either artificial or platform reef sites. This effect was evident in both the EEZ and TTS, although the average fish was larger in the EEZ as smaller fish are typically found around nearshore structures.

TPWD has been routinely monitoring our inshore fish populations in the bays for over 40 years, and we use this data to observe important trends. While the sampling timeline is much shorter for our offshore adult fish populations, this vertical longline survey is an important step towards better management of these offshore fisheries. Continuing to routinely sample these offshore waters will ensure we can identify and address any changes to these populations in the future.