Some thinking out loud here: this line is rather eye-catching as it is wedged between a conglomeration of lines from other texts. The only parts of the stanza that aren't directly "snatched" from another source are several lines above: "I sat upon the shore / ... / Shall I at least set my lands in order?" From this, a close reading would be most helpful to understand the overall conclusion of the poem.
Firstly, "these fragments" seem to be less cryptic than the rest of the poem: the narrator refers to the lines from other texts—Dante, De Nerval, Kyd, Hindu philosophy, etc.—that precede and follow this line. "Shore," however, has a double-meaning. The first line of the stanza describes the narrator sitting upon a shore (noun), yet the narrator is also shoring—or supporting something (often by holding it up) that would otherwise fail/topple. The fragments are being shored—they are being saved, in a way, from decline or irrelevance; in fact, they already have ("I have shored"). To recap: at the same time that the narrator is "fishing" "upon the shore," the narrator is "shoring" the fragments. The narrator shores these fragments by fishing them out of water; they are saving them from water. Perhaps they are saving them from drowning by fishing them out.
This reminds me of two text references: one, the man at the bottom of the lake in Marie Larisch's "My Past," who "will return" from the bottom of the lake by rising from the dead. In a way, these fragments may be rising from the dead, too, thanks to the narrator. Secondly, from today's reading, the Weston analysis of the Fisher King, who has a "devotion to the pastime of fishing." The text contains a lot of important information, but I see the Fisher King as having two important characteristics. One: "the guardian of the Grail bears the title of Fisher King." This relates to the "third figure," like the "third officer" Shackleton was, whose job is to be a guardian in the first place. In this thread, the Fisher King represents a "third figure" of sorts. The Fisher King looks after—or guards—the Holy Grail, an object that grants immortality to the user. Thus—the Fisher King bars anyone from achieving immortality and constrains everyone to the inevitability of death. This can align with a second description of the Fisher King, toward the end of the Weston text. The Fisher King is
not merely a deeply symbolic figure, but the essential centre of the whole cult, a being semi-divine, semi-human, standing between his people and land, and the unseen forces which control their destiny.
The Fisher King plays an intermediary role—he connects the mortal with the divine; in a way, connecting life and death. Life and death can be thought of as two sides of the same coin (in other words, if death didn't exist, then the conception of life wouldn't exist as well). By ensuring death, the Fisher King ensures life in turn—and vice-versa. If this narrator is the Fisher King, or someone akin, then the "fragments" being saved may be the fragments of life itself.
The final part of this line is "against my ruins," and the idea of "ruins" is mentioned numerous times in today's reading. The ruins are not the same as the fragments—they are not being supported, or upheld—but instead, the fragments are being saved against them (in contrast, or opposition, to them). Most notably, "ruins" are mentioned in the De Nerval text:
... the prince of Aquitaine, his tower in ruins...
Notably enough, this quote (in French) comprises the line exactly above this one. The ruins themselves are those of the tower, which reminds me of the Tower tarot reading. The Tower tarot foreshadows "massive change, upheaval, destruction and chaos" (Biddy Tarot). So, in spite of—or in opposition to—this massive change, destruction, and chaos, these "fragments" have been shored up; they have been fished out; they have been saved and preserved. The destruction in question may refer to many things—it may refer to that of WW1, or the decline in religious piety, or the destruction of nature in favor of urbanization (or all three of these). From this destruction are fragments—represented by the lines of text from other sources—that save the core principles of human life. Going back to the Fisher King analysis, what is saved may be the cycle of life and death. Though urbanization and war seem to defy this cycle (the ability to construct and destruct by one's own accord), the Holy Grail is still protected.
Other notes I don't have the space to mention: connections to the illusion of life by Bradley; connections to the idea of memory (preserving memory) from Webster; the idea of planting and eating vegetation; The Golden Bough.