The most widely used output-based physical measure of fishing capacity is hold capacity. Those who have used this approach include Rothchild (1972), Carlson (1973), Gertenbach (1973), Prochaska (1978), Siegel et al. (1979), Herrick (1979), Flam and Storoy (1982), Wallace and Brekke (1986), Wilen (1989), Vestergaard and Frost (1994), Anderson (1994), Flaaten, Heen, and Salvanes (1995) and Vestergaard (1996).
DFO (n.d.) notes that hold capacity as a measure of maximum possible output requires information on the number of vessels, their hold size, and the number of full-hold trips per year. Hold capacity of vessels may be less accurately measured than vessel length (Southwest Region, 1993). Assuming that the goal of vessels is to bring in a full vessel when possible implicitly assumes that vessels attempt to produce maximum output, since maximizing catch does not necessarily maximize profits or revenues and ignores other constraints such as weather, fish availability, quantity or quality controls on catch or fishing time, and also overlooks the multispecies nature of many fisheries. Vessel and hold information may frequently be readily available, but estimating the maximum number of trips per year is difficult, especially as technological change impacts on trip potential by decreasing search and catch time.
When hold capacity is used, marine architects and marine surveyors canvassed by the Southwest Region of the U.S. National Marine Fisheries Service (1993) reported several considerations. All engine rooms, lazarettes, water storage, dry hold, deck or any other space that can be converted must be excluded. Storage must be carefully defined and certification required. Since different fish pack at different densities and it is unlikely that all vessels will use 100 percent of the hold 100 percent of the time, the hold capacity may provide a higher number than needed. Two marine architects suggested making some sort of correlation between the landings and the hold capacity in deriving a figure. Five marine surveyors agreed that length is important in allowing fishers to venture further and for a longer period of tie, but ultimately, it is the quantity and quality of fish that vessels can bring back that determines how much they will fish. Three marine surveyors agreed that fish-hold capacity is a good indicator of harvesting capacity and is the traditional method used, while two indicated that no correlation could be made. Of those surveyors indicating that hold capacity was a good indicator, they felt that hold capacity, when used alone, may be too high. They suggested some correlation between the hold and the landings to obtain some sort of efficiency ratio. Having calculated the hold, it is possible to convert it to tonnage by using density ratios.
Herrick (1979) and DFO (n.d.) noted other limitations to this approach: (1) labor and equipment may constrain catch before hold capacity; (2) estimating the maximum number of trips per year can be difficult; (3) fish quality considerations could dictate a return to port before the hold is full. Kenchington and Charles (1989) further noted that smaller fishing boats may not have an actual hold and that some larger ones will harry home a deck cargo in addition to a hold full of fish if catch rates permit. Kenchington and Charles (1989) further observe that many fisheries operate under trip regulations which constrain the permitted landings to less than hold capacity. As a consequence, there can be no general link between hold capacity and fishing capacity.
The approach may be difficult to apply when there are catcher-processors. Fish caught are not generally stored whole, but are instead immediately processed. Smith and Hanna (1990) also observe that when discussing multispecies and multipurpose fisheries, this concept of capacity becomes problematic.