During a fortnight spent at Ancon (11° 45ʹ S.), between January 27 and February 10, I paid considerable attention to the local climatic conditions, and especially to the temperature of the inshore water. The daily range of the air-temperature was only five or six degrees, the average minimum and maximum being 71° and 75·9°, and the mean for the period 73·5°. The mean temperature of the surface-water at the head of the pier, from observations taken at about 7 a.m. and 4 p.m., was 68·6°, or five degrees cooler than the air, the mean temperature in the morning being 69·1° and in the afternoon 68°.

Observations on the Temperature of the Humboldt or Peruvian Current

(Made by H. B. Guppy, January to March, 1904.

Those at Panama are added for the sake of comparison)

Locality. Depth (fathoms).Distance from shore (miles).S. lat.Date.Hour.Depths in fathoms: temperature in Fahrenheit degrees.
Surface.1.2.3.4.5.6.7.8.9.10.11.12.13.14.15.16.17.18.19.20.21.22.
Antofagasta222⁄323°40ʹ Jan. 125 p.m.71°70°...............61°......57°...............56°..................
Jan. 136 a.m.70.........................................................55......
Tocopilla181⁄222 0Jan. 148 a.m.57...........................56...............55..................
Iquique92⁄320 15Jan. 155.30a.m.59............58.........55.......................................
Pisagua101⁄219 30Jan. 168 a.m.57·5...........................56....................................
Arica...1⁄418 25Jan. 167 p.m.66.....................57..........................................
Mollendo221⁄3 17 0Jan. 178 a.m.61·5.....................57..........................................
17 0Jan. 176 p.m.65...........................59....................................
17 0Jan. 189.30a.m.62............57·5............57............56..................55
Callao5112 3Jan. 206 a.m.60·5............58·5...................................................
Ancon1713⁄411 45Jan. 2911 a.m.66......6·15...58·5......57...57..................56·5...............
Salaverri63⁄48 15Febr. 216.30p.m.65...............62................................................
Eten71⁄27 0Febr. 226 a.m.66·5..................63.............................................
Payta 1611⁄2 5 0Febr. 239 a.m.70..................67·5.....................62·5.....................
Puerto Bolivar1013 10Mar. 7noon78............71·5............70....................................
Panama83 (8 50)Mar. 234 p.m.82..................79·5.............................................
( N.)Mar. 247 a.m.79·5.....................79·5..........................................

The Ancon climate at this period is full of oddities and abnormalities, and in this way typifies much of the coast of Peru. Thus, since the heat of the day is tempered by the cool south-westerly winds which die away in the evening and give place usually to warm, light, northerly and north-westerly breezes, there is, as above remarked, but a small difference between day and night temperatures. The coldest time of the twenty-four hours is not in the early morning but at sunset. The sea off the beach is, on the average, much cooler than the air, which is not a normal state of things; and again, the water is often two or three degrees colder in the evening than it is in the morning, which is very unusual. Though the sea-border is practically a desert for the greater part of the year and has no rain, it is frequently enveloped in drizzling fogs or “garuas.” Judged from a European standard, things go by contraries on the coast of Peru; and this is entirely the effect of the Humboldt Current.

The temperature of the inshore waters of Ancon Bay varied considerably during the twenty-four hours. During the day, with the prevailing southerly wind, the cool waters of the current had free access to the bay, and swept around its border in their course north; but in the night, when northerly breezes occurred, the cold waters of the current were pushed off the coast and their place taken by the warmer inshore waters from the north; and this sometimes continued for a day or two. When the current again got mastery and its clean, cool waters filled the bay, the temperature of the water dropped suddenly five or six degrees, and the bay was filled with fish. At such times men in boats leave the beach, and in a few minutes, with hand-nets and baskets, they obtain thousands of the small fry. Other men, fishing with lines from the pier-head, seem ill-contented unless they can catch fish of the size of small mackerel at the rate of one a minute.

There can be little doubt that on the coasts of Chile and Peru the instincts of fish often lead them astray, on account of the sudden changes of temperature arising from the conflict between the warmer waters of the open sea and the cooler waters of the current. From the preceding remarks it will be inferred that sometimes the current is pushed off the coast for a while and its place taken by the warm waters from the north. At other times it dives down, so to speak, and flows at a deeper level, and warmer waters prevail both out at sea and inshore. At other times again, and this must be most disconcerting to the fish, the cold current suddenly appearing at the coast predominates at the surface for days together, and we have stretches of coast which, although lying within tropical latitudes, are washed by waters having the temperature of the temperate zone. It is to such causes that we must attribute the reckless habits of fish on these coasts. They are known to throw themselves on the beaches in thousands, where by their decay they taint the air long afterwards. Mr. Anderson Smith in his recent book on Temperate Chile vividly describes what goes on on such occasions at the port of Valdivia. At times the scene must be indeed a strange one, since huge octopi are rolled up on the beaches in numbers, and are regarded by the indigenes as deliberately seeking their death. Whether they commit suicide or not, “their beaks that blacken the edge of the sea-wash in places” afford a melancholy proof that their instinct has blundered.

The Mode of Observation.—A thermometer made on the Sixe pattern which I used several years ago for taking the bottom-temperatures of rivers, was employed for the deeper temperatures, and at critical depths the observations were always repeated. This instrument was compared after each set of observations with an ordinary thermometer graduated on the stem, which was compared with my standard thermometer provided with a Kew certificate.... The observations in the Panama Roadstead have been added for the sake of contrast.

NOTE 75 (page [496])
On the Stranded Massive Corals apparently of the Genus Porites found on the Coast of Peru and North Chile, at Arica (18° 25ʹ S.), Callao (12° 3ʹ S.), and Ancon (11° 45ʹ S.)