Mortality

Curtis (1990) examined the population dynamics related to the recovery of an offshore Lake Trout population near Stannard Rock, Lake Superior. As part of this study, mortality rates were estimated from the relative abundance of Lake Trout longer than 43.2 cm. Relative abundance was recorded as the catch-per-unit-effort (CPE) of each age group in each year expressed as the number of fish caught per 50,000 m of 114.3 mm mesh gillnet. The results are shown in the table below. [Note: (1) the values in the table have been rounded to integers; (2) values recorded as “tr” in the original paper were recorded as “0.5” in this table; and (3) the years of capture are not contiguous (there is a break between 1959 and 1963 and again between 1969 and 1973).]

 

Year	VI	VII	VIII	IX	X	XI	XII	XIII	XIV
1959	64	219	241	121	33	9	1	0.5	1
….	.	.	.	.	.	.	.	.	.
1963	129	339	331	192	70	16	0.5	0.5	0.5
1964	149	524	515	201	63	18	2	0.5	0.5
1965	75	379	501	328	133	39	11	1	0.5
1966	149	488	459	172	64	22	5	0.5	0.5
1967	63	368	287	130	55	19	6	0.5	0.5
1968	50	215	259	141	55	18	5	1	0.5
1969	45	150	153	76	23	6	0.5	0.5	0.5
….	.	.	.	.	.	.	.	.	.
1973	101	759	1268	1116	491	141	40	4	0.5
1974	151	733	1114	1092	571	163	50	9	5
1975	109	901	1517	1606	1076	342	117	12	7
1976	53	604	1204	1560	1146	396	156	18	10
1977	157	867	1343	1410	1031	417	192	17	7
1978	89	735	1307	1623	1150	445	198	18	14
1979	29	299	718	1268	1195	585	300	36	14

 

Use these results to answer the following questions.

1. What year-class of fish is represented by the 339 age-VII fish caught in 1963?
2. Show the data frame of catches and corresponding ages for the following groups of fish.
   1. For fish captured in 1963.
   2. For fish of the 1963 year-class.
   3. The earliest year-class that is fully represented for ages IX through XII.
   4. The latest year-class that is fully represented for ages IX through XII.
3. For each data frame created above, identify whether the data represent a cross-sectional or longitudinal catch curve.
4. For the third data frame created above (earliest year class).
   1. Estimate, with 95% confidence interval, the instantaneous total mortality rate using the catch-curve regression method for ages IX through XII.
   2. Estimate, with 95% confidence interval, the annual total mortality rate using the catch-curve regression method for ages IX through XII. Carefully interpret this result.
5. Repeat the previous question for the last data frame created above (latest year class).
6. Determine if the instantaneous mortality rate is significantly different between the earliest and latest year-classes that are fully represented for ages IX through XII.

 

Solution Code:

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References

Curtis, G. L. 1990. Recovery of an offshore Lake Trout (Salvelinus Namaycush) population in eastern Lake Superior. Journal of Great Lakes Research 16(2):279–287.

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