California Department of Fish and Game: a part of the State of California Resources Agency. It is responsible for managing the states’ "living" resources, including those within the marine environment. The Department works closely with the National Marine Fisheries Service (NMFS), especially regarding harbor seals and other pinnipeds.

Carrying Capacity: describes the capability of a particular environment or habitat to support a "maximum" population of animals and/or plants. The concept of "carrying capacity" incorporates: 1) physical space, 2) food and/or nutrient availability, 3) waste removal/recycling, 4) mortality factors, 5) time or temporal factors, and 6) other factors.

El Niño: an oceanographic event in the Pacific Ocean in which warmer than normal water occurs throughout much of the eastern Pacific Ocean primarily north of the equator. An El Niño generally lasts many months and causes major shifts in fish populations and plankton.

Endangered Species Act (ESA): enacted by the U.S. Congress in 1973 with the intent of providing special protection to those plants and animals that have undergone severe population declines. Species declared to be "threatened" or "endangered" have extra legal protection and special management procedures designed to restore their population to healthy and sustaining levels. The U.S. Fish and Wildlife Service and other federal and state resource agencies enforce the ESA.

Gillnets: flexible ("flimsy") large mesh fishing nets that are set in a straight line in a location for many hours, usually overnight. In theory, larger targeted fish swim into the net with only their heads passing through the mesh. The flimsy net twine "tangles" with the fish’s gill plates and they become "trapped." Supposedly, smaller fish swim through the net without becoming entangled. However, gillnets generally capture many non-targeted species. They were a major source of pinniped and sea otter mortality along the California coast.

Hubbs-SeaWorld Research Institute (H-SWRI): this research organization studies a wide variety of marine animals, habitats, and phenomena. It is based in San Diego and is supported by SeaWorld plus a variety of research grants from state and federal agencies and charitable entities. It is named after Carl Hubbs, a world-renowned marine ichthyologist (person who studies fish).

Marine Mammal Protection Act (MMPA): enacted by the U.S. Congress in 1972 to provide special legal status for all marine mammals (which include seals, walruses, dolphins, sea otters, manatees, etc.) Some marine mammals are also additionally protected under the Endangered Species Act (ESA), e.g., humpback whales, sea otters, etc. Both harbor seals and California sea lions are protected by the MMPA but have no ESA status. The National Marine Fisheries Service and other federal and state resource agencies enforce the MMPA.

National Marine Fisheries Service (NMFS): a federal resource agency within the Department of Commerce. Its primary responsibility is the management of fisheries within the U.S. Economic Zone that extends 200 miles beyond the coast. Relative to pinnipeds, the NMFS enforces the MMPA.

Optimum sustainable population (OSP): the maximum numbers or size of a population that can be maintained on a continuing basis. This OSP concept is related to "carrying capacity" with the "time" factor usually being measured in years. Regarding harbor seals, the California population appears to be approaching its OSP.

Pinnipeds: marine mammals characterized by fur/hair, four limbs modified for swimming (flippers), breath held while diving, generally coming ashore in colonies for reproduction. Includes harbor seals, sea lions, walruses, elephant seals, and other seals.

Rookery: it is usually used to describe a location with a group of pinnipeds on shore for the purposes of reproduction. A typical seal rookery would have adult males and females, juveniles and pups. The term rookery has neither quantitative nor legal definition relative to pinnipeds. It is also used to describe any breeding ground for birds and mammals.

Seal Rock Marine Mammal Reserve (SRMMR): an area slightly offshore of La Jolla (City of San Diego), California. Established in 1994 by the City of San Diego to provide additional protection for harbor seals on Seal Rock.

Sexually dimorphic: a biological term used to describe external differences between males and females of the same species. For example, many bird species are sexually dimorphic with the males being bigger and more colorful than the females. Relative to harbor seals, there are no obvious external differences between males and females and, thus, they are not sexually dimorphic. Sexual dimorphism is evident in California sea lions with the males being much larger and having a bulging forehead.