Longline Surveys

map of longline survey area - Gulf of Mexico and North Atlantic
Longline sampling area
Credit: SEFSC

Mission: To conduct longline surveys to monitor interannual variability of shark populations of the Atlantic coast and the Gulf of Mexico.

Longline gear

The fishing gear used in this survey consists of a 4.0mm diameter monofilament mainline of 1 nm in length. A gangion of 3.6m length is deployed every 18.3m along the mainline. Gangions consist of 3.0mm diameter monofilament line with #15 circle hooks. The mainline has radar reflector buoys attached at each end and is held stationary on the bottom with three 5 kg weights at start, middle and end of the mainline. The gear is baited with Atlantic Mackerel (Scomber scombrus) and the gear is allowed to soak for 1 hour.


longline fishing gear illustration
Longline fishing gear
Credit: SEFSC
longline monofilament
Longline monofilament
Photo Credit: SEFSC

CTD (Conductivity Temperature Depth)

The CTD provides a surface to bottom profile of temperature, salinity, dissolved oxygen, chlorophyll, turbidity and depth.

Length-Weight-Sex

weighing a shark
Measuring a tiger shark
Photo Credit: SEFSC

Shark measurements can include total length, fork length, stretch-total length and precaudal length. A landing sling is often used for large sharks to facilitate measurements and weights.

The sex is recorded and the stage of sexual development is determined for males. Males have external structures that become calcified with maturity and stage can be assigned based on the size and flexibility of the clasper.

measuring shark length
Measuring a Shark
Photo Credit: SEFSC


Tagging Sharks

Sharks are tagged with two types of tags. The first tag, Roto-tag, is for small sharks; M-tags, are generally used on large sharks. The small Roto-tags are attached to the first dorsal fin and the M-tags are imbedded in the muscle along the dorsal fin base.