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The main cause of the decline of loggerhead turtles, and the current primary threat to global populations is bycatch in longlines, gillnets, trawls, traps and pots, and dredges. Loggerhead can be hooked in the mouth or another part of their body when trying to consume bait, entangled in gillnets or ropes, or caught in a trawl or dredge. Longlines, gillnets, and trawls are responsible for the majority of sea turtle bycatch events around the world (Wallace et al, 2010). Commercial longlines incidentally caught an estimated 200,000 loggerhead turtles in 2000 (Lewison et al, 2004).

Gillnet fisheries pose the greatest threat to the vaquita population. Current bycatch estimates are unavailable, but in the early 1990s an estimated 39 to 84 individuals were caught by fishermen from one town (D'Agrosa et al 2000).  In 2014, CIRVA reported that probably only 100 individuals remain of this species, and the population was projected to continue declining without emergency regulatory action by the Mexican government (CIRVA, 2014). By 2019, only ~19 individuals are estimated to remain. Recent surveys indicate a population low of ten individuals .

The main threat to the franciscana is bycatch in gillnet fisheries in its native coastal waters of Argentina, Brazil, and Uruguay.   

Non-target benthic invertebrates are caught as bycatch in huge volumes, but precise numbers are not available.

Bycatch of pilot whales (short-finned) occurs in the pelagic longline fisheries targeting swordfish, tuna, and shark in the U.S. Mid-Atlantic.  There are also records of pilot whales (long and short-finned) being taken in gillnet, trawl, and purse seine fisheries. "Whale-safe" hooks are being tested in the longline fishery that aim to reduce pilot whale bycatch by allowing whales to straighten the hook, while being strong enough to retain target catch.   

Bycatch of pilot whales (short-finned) occurs in the pelagic longline fisheries targeting swordfish, tuna, and shark in the U.S. Mid-Atlantic.  There are also records of pilot whales (long and short-finned) being taken in gillnet, trawl, and purse seine fisheries. "Whale-safe" hooks are being tested in the longline fishery that aim to reduce pilot whale bycatch by allowing whales to straighten the hook, while being strong enough to retain target catch.   

Chatham albatross are caught in a variety of longline and trawl fisheries in the southeast Pacific Ocean.  Known mortality from bycatch has been observed in ling demersal and tuna pelagic longline fisheries (Robertson et al 2004) and hake and orange roughy trawl fisheries in the New Zealand Exclusive Economic Zone (EEZ) (Baird 2004a; 2004b).

The small population of North Atlantic right whales is in danger of extinction. These whales were hunted nearly to extinction by commercial whalers by the end of the 1700s, but today are at risk from entanglement in fishing gear and boat strikes.   

The dusky shark is currently listed as Vulnerable by the IUCN, but populations continue to decline. The dusky shark is one of the slowest-growing, latest-maturing sharks, bearing small litters after a glong gestation period. These characteristics make the shark especially vulnerable to depletion by fisheries. In the Northwest Atlantic, dusky sharks began to decline in the 1970s, when they were targeted by recreational fishers. They continued to decrease due to directed catch in US shark fisheries in the 1980s.

Although it is believed that the harbor porpoise population is not seriously in danger at present, incidental catch of the species in gillnets continues to be the primary threat throughout its range (Hammond et al 2008). Off the eastern coast of the US, an estimated 1200 to 2900 harbor porpoises were killed annually in gillnets between 1990 and 1996 (Waring et al 1998). In the North Sea, Danish annual estimates of bycatch ranged from 2867 to 7566 between 1990 and 2002 (Vinther & Larsen 2002).

The once-abundant Mediterranean monk seal has been adversely impacted by human activities, ranging from exploitation for fur and oil to habitat fragmentation that have occured over many centuries. Today, one of the greatest threats facing the remaining seals is accidental entanglement in fishing nets. Bycatch mortality occurs throughout the species' range, and has been increasingly problematic since the 1980s (Guclusoy et al 2004).

Historically, the Chilean dolphin has been hunted both for food and for crab bait (Reeves et al 2008). Although cetaceans are now protected by law in Chile (Torres et al 1979), regulation enforcement is virtually nonexistent and temptation is high for impoverished fishermen to supplement their income by killing dolphins for bait (Dawson 2009; Reeves et al 2008).

The principal threat to the Irrawaddy dolphin throughout much of its range is accidental entanglement in gillnets (Smith et al 2007). Freshwater populations of the species are at the most risk, particularly those inhabiting the Mekong River (Cambodia, Lao PDR, Vietnam), the Mahakam River (Indonesia), the Ayeyarwaddy River (Myanmar), and lakes Chilika (India) and Songkhla (Thailand). These areas are considered high-use habitat due to their biological productivity, and there is frequently overlap between dolphin populations and gillnet fisheries (Smith et al 2006).