Fish kill dead zones in the gulf are mainly created by the nitrogen and phosphorus enrichment of the Lower Mississippi River. Some species of fish exhibit mass simultaneous mortality as part of their natural life cycle. Fish kill due to spawning fatalities can occur when fish are exhausted from spawning activities such as courtship, nest building, and the release of eggs or milt (sperm). Fish are generally weaker after spawning and are less resilient than usual to smaller changes in the environment. Examples include the Atlantic salmon and the Sockeye salmon where many of the females routinely die immediately after spawning. A
Fish tug the 1930s it became common to add a pilothouse amidship or near the stern, and to continue the cabin covering to the bow in what was known as a "sprayhood." Steel-hulled boats began to replace wooden-hulls in the late 1950s. Beginning in the 1970s, new regulations began to greatly restrict gill-net fishing, making the fish tug all but obsolete. The few fish tugs that remain in use today are largely objects of historical preservation efforts and not under commercial ownership. Fish tug A fish tug (sometimes called fishtug, fish tugboat, fishing tug, etc.) is a type of boat that was