The spawning stock biomass (SSB) of the stock gets calculated from the survivors of the previous year. This provides a value for the first year after the end of the object. Weights-at-age, maturity in this extra year are calculated as averages over the last wts.nyears.
Arguments
- x
An FLStock object containing estimates of abundance and harvesting.
- fbar
The Fbar rate assumed on the extra year. Defaults to 0.
- wts.nyears
Number of years in calculation of mean weight-at-age and maturity for the extra year.
- fbar.nyears
Number of years in calculation of mean selectivity, natural mortality and fraction of F abnd M before spawning for the extra year.
Details
For stocks spawning later in the year, a value for the average fishing mortality, fbar, expected in that year can be provided. Mortality until spawning is then calculated, with M and selectivity assumed in the extra year to be an average of the last fbar.nyears.
Examples
data(ple4)
ssb_next(ple4)
#> An x of class "FLQuant"
#> , , unit = unique, season = all, area = unique
#>
#> year
#> age 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967
#> all 355374 362120 380052 391385 482245 440658 430475 383583 404516 473937
#> year
#> age 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977
#> all 458977 402865 370473 361610 366129 302365 298094 301757 328726 329116
#> year
#> age 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987
#> all 327543 302271 319089 290780 284211 339238 367251 394666 407972 470953
#> year
#> age 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
#> all 424696 448230 396458 356947 311431 279962 233481 222203 203391 204948
#> year
#> age 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007
#> all 237863 219149 230902 234211 221902 248312 233477 253737 284447 293330
#> year
#> age 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017
#> all 371837 453027 554244 575459 617538 709948 823276 774157 836453 913289
#> year
#> age 2018
#> all 980986
#>
#> units: t
# Compare with ssb()
ssb(ple4)[, ac(2014:2017)] / ssb_next(ple4)[, ac(2014:2017)]
#> An x of class "FLQuant"
#> , , unit = unique, season = all, area = unique
#>
#> year
#> age 2014 2015 2016 2017
#> all 1 1 1 1
#>
#> units: