Length-weight Relationships for 83 Reef and Bottomfish Species from the Commonwealth of the Northern Mariana Islands

Length and weight are two fundamental metrics used in studying fishes and almost any other living organism. The allometric growth equation (Weight = a * Lengthb) is typically used to define the algebraic relationship between increases in fish length and weight. Once developed, this formula can be used to estimate weight with respect to length, or vice versa. For example, in creel surveys conducted by the Commonwealth of the Northern Mariana Islands (CNMI) Division of Fish and Wildlife (DFW), the catch is rarely weighed in the field. To limit the time requested of fishermen, fish and invertebrates are quickly measured (Oram et al., 2010a; Oram et al., 2010b), and an estimated weight is calculated later. When length measurements are entered into the computer, missing weights are estimated based on known allometric growth formulas, either derived locally (1st choice) or from the literature for other regions (2nd choice). Very little information has been published in the scientific literature regarding length-weight relationships for marine species in the CNMI (e.g., Graham, 1994; Ralston, 1988). This study analyzes length-weight data collected from two small-scale commercial fisheries from the CNMI: the night free-diving spear and bottomfish fisheries. This report summarizes allometric growth relationships for 83 fish species and two invertebrates for which sufficient data were available.